@misc{21422, author = {Sunko, Veronika}, publisher = {Institute of Science and Technology Austria}, title = {{Data underpinning "Magneto-optical Kerr effect in an A-type antiferromagnet"}}, doi = {10.15479/AT-ISTA-21422}, year = {2026}, } @article{21436, abstract = {The cobalt-intercalated transition metal dichalcogenide CoxTaS2 hosts a rich landscape of magnetic phases that depend sensitively on x. While the stoichiometric compound with x = 1/3 exhibits a single magnetic transition, samples with x≤0.325 display two transitions with an anomalous Hall effect (AHE) emerging in the lower temperature phase. Here, we resolve the spin structure in each phase by employing a suite of magneto-optical probes that include the discovery of anomalous magneto-birefringence: a spontaneous time-reversal sensitive rotation of the principal optic axes. A symmetry-based analysis identifies the AHE-active phase as an anisotropic (2+1)Q state, in which magnetic modulation at one wavevector (Q) differs in symmetry from that at the remaining two. The (2+1)Q state naturally exhibits scalar spin chirality as a mechanism for the AHE and expands the classification of multi-Q magnetic phases.}, author = {Kruppe, Jonathon and Rodriguez, Josue and Xu, Catherine and Analytis, James and Orenstein, Joseph and Sunko, Veronika}, issn = {2397-4648}, journal = {npj Quantum Materials}, publisher = {Springer Nature}, title = {{Anisotropic multi-Q order in CoxTaS2}}, doi = {10.1038/s41535-026-00856-w}, year = {2026}, } @unpublished{21438, abstract = {Antiferromagnets (AFMs) hold promise for applications in digital logic. However, switching AFM domains is challenging, as magnetic fields do not couple to the bulk antiferromagnetic order parameter. Here we show that magnetic-field-driven switching of AFM domains can in many cases be enabled by a generic reduction of magnetic exchange at surfaces. We use statistical mechanics and Monte Carlo simulations to demonstrate that an inequivalence in magnetic exchange between top and bottom surface moments, combined with the enhanced magnetic susceptibility of surface spins, can enable deterministic selection of antiferromagnetic domains depending on the magnetic-field ramping direction. We further show that this mechanism provides a natural interpretation for experimental observations of hysteresis in magneto-optical response of the van der Waals AFM $\mathrm{MnBi_2Te_4}$. Our findings highlight the critical role of surface spins in responses of antiferromagnets to magnetic fields. Furthermore, our results suggest that antiferromagnetic domain selection via purely magnetic means may be a more common and experimentally accessible phenomenon than previously assumed.}, author = {Weber, Sophie F. and Sunko, Veronika}, booktitle = {arXiv}, title = {{Deterministic domain selection of antiferromagnets via magnetic fields}}, doi = {10.48550/arXiv.2601.06646}, year = {2026}, } @unpublished{21703, abstract = {Altermagnetism has recently emerged as a distinct class of collinear antiferromagnets that break time-reversal symmetry, exhibiting a host of novel properties. Applied strain has attracted particular attention as a key tuning parameter for altermagnets. Although several experimental studies have demonstrated the preparation of single-domain states through a combination of applied strain and magnetic field, the route to such states remains unclear. Here, we use magneto-optical measurements on single crystals of MnTe under applied strain to show that, in contrast to previous reports, strain acts primarily to rotate the Néel vector L continuously. Since the orientation of L determines the magnetic point group symmetry, this continuous rotation effectively tunes the symmetry and its associated physical properties. Furthermore, we demonstrate that built-in strain in free-standing crystals is sufficient to pin L into continuous textures over millimeter length scales. Together, these results provide guidance for future device design and open the door to leveraging the Néel vector orientation as a tunable degree of freedom in spintronic applications.}, author = {Alex Liebman-Peláez, Alex Liebman-Peláez and Kruppe, Jon and Regmi, Resham Babu and Ghimire, Nirmal J. and Sun, Yue and Mazin, Igor I. and Noad, Hilary M. L. and Analytis, James and Sunko, Veronika and Orenstein, Joseph}, booktitle = {arXiv}, title = {{Strain continuously rotates the Néel vector in altermagnetic MnTe}}, doi = {10.48550/arXiv.2604.07653}, year = {2026}, } @article{21872, abstract = {Magneto-optic Kerr effect (MOKE) is a powerful probe of broken time-reversal symmetry (T), typically used to study ferromagnets. While MOKE has been observed in some antiferromagnets (AFMs) with vanishing magnetization, it is often associated with structures whose symmetry is lower than basic collinear, bipartite order. In contrast, theory predicts a mechanism for MOKE intrinsic to all AFMs of A-type, i.e. layered AFMs in which ferromagnetic layers are antiferromagnetically aligned. Here we report the experimental confirmation of this mechanism in a bulk AFM. We achieve this by measuring the imaginary component of MOKE as a function of photon energy in MnBi2Te4, an A-type AFM where T is preserved in combination with a translation, and comparing the experimental results with model calculations. Our model suggests that observable MOKE should be expected in all collinear A-type AFMs with out-of-plane spin order, thus enabling optical detection of AFM domains and expanding the scope of MOKE to few-layer AFMs.}, author = {Sunko, Veronika and Ahsanullah, Salman and Jain, Vivek and Weber, Sophie and Kumaran, Sivaloganathan and Yan, Jiaqiang and Orenstein, Joseph and Ovchinnikov, Dmitry}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Magneto-optical Kerr effect in an A-type antiferromagnet}}, doi = {10.1038/s41467-026-72577-4}, year = {2026}, } @article{22116, abstract = {Magnets with isotropic easy-plane symmetry host Goldstone modes that can be leveraged for efficient spin transport. Here, we present a time-resolved optical polarimetry technique that allows us to detect and characterize such low-frequency modes, and use it to observe the Goldstone mode in the multi-Q broken helix phase of EuIn2As2. The strength of our technique comes from the ability to distinguish between nematic and magnetization dynamics in order to yield information about the mode structure, in addition to its frequency. We find that the nearly uniform spin precession characteristic of a Goldstone mode is realized only when a small magnetic field is used to unpin the broken helix from local strain generated during crystal growth. In this regime, the mode frequency scales linearly with the applied field due to the ground state C2z symmetry of the broken helix. Our work shows how optical polarimetry can be used to study the Goldstone modes of complex magnets.}, author = {Liebman-Peláez, A. and Garratt, S. J. and Sunko, Veronika and Sun, Y. and Soh, J. R. and Prabhakaran, D. and Boothroyd, A. T. and Orenstein, J.}, issn = {2469-9969}, journal = {Physical Review B}, number = {22}, publisher = {American Physical Society}, title = {{Observation of a Goldstone mode in the broken helix by time-resolved optical polarimetry}}, doi = {10.1103/b48p-kw5l}, volume = {113}, year = {2026}, } @article{21437, abstract = {Altermagnets are a class of collinear magnets that exhibit non-relativistic spin splitting (NRSS) of electronic bands in the absence of net magnetization. Their potential to generate large spin polarization without spin-orbit coupling has created strong interest in probes that access the underlying order parameter directly. In this Perspective, we show that linear magneto-birefringence (LMB) provides a natural and broadly applicable route to detecting altermagnetic order. Building on the correspondence between the momentum-space structure of NRSS and the ferroic ordering of magnetic multipoles in real space, we demonstrate how $d$-wave and $g$-wave NRSS textures yield distinct LMB responses. We present a symmetry-based framework that identifies the optical geometries and field configurations required to isolate specific multipole components, enabling domain imaging and providing benchmarks for theoretical models of LMB.}, author = {Sunko, Veronika and Orenstein, J.}, issn = {2397-4648}, journal = {npj Quantum Materials}, publisher = {Springer Nature}, title = {{Linear magneto-birefringence as a probe of altermagnetism}}, doi = {10.1038/s41535-026-00901-8}, year = {2026}, } @article{21431, abstract = {Several optical experiments have shown that in magnetic materials, the principal axes of response tensors can rotate as an odd function of an applied magnetic field. Here we offer a microscopic explanation of this effect, and we propose a closely related dc transport phenomenon—an off-diagonal symmetric conductivity, linear and odd in a magnetic field, which we refer to as linear magnetoconductivity (LMC). Although LMC has the same functional dependence on a magnetic field as the Hall effect, its origin is fundamentally different: LMC requires time-reversal symmetry to be broken even before a magnetic field is applied, and is therefore a sensitive probe of magnetism. We demonstrate LMC in three different ways: via a tight-binding toy model, a density functional theory calculation on MnPSe3, and a semiclassical treatment. The third approach identifies two distinct mechanisms yielding LMC: momentum-dependent band magnetization and Berry curvature. Finally, we propose an experimental geometry suitable for detecting LMC, and we demonstrate its applicability using Landauer-Büttiker simulations. Our results emphasize the importance of measuring the full conductivity tensor in magnetic materials, and they introduce LMC as a new transport probe of symmetry.}, author = {Sunko, Veronika and Liu, C. and Vila, M. and Na, I. and Tang, Y. and Kozii, V. and Griffin, S. M. and Moore, J. E. and Orenstein, J.}, issn = {2469-9969}, journal = {Physical Review B}, number = {13}, publisher = {American Physical Society}, title = {{Linear magnetoconductivity as a probe of time-reversal symmetry breaking}}, doi = {10.1103/33ns-8gwj}, volume = {112}, year = {2025}, } @article{21432, abstract = {The interplay between symmetry and topology in magnetic materials makes it possible to engineer exotic phases and technologically useful properties. A key requirement for these pursuits is achieving control over local crystallographic and magnetic structure, usually through sample morphology (such as synthesis of bulk crystals versus thin films) and application of magnetic or electric fields. Here we show that V1/3NbS2 can be crystallized in two ordered superlattices, distinguished by the periodicity of out-of-plane magnetic intercalants. Whereas one of these structures is metallic and displays the hallmarks of altermagnetism, the other superlattice, which has not been isolated before in this family of intercalation compounds, is a semimetallic noncollinear antiferromagnet that may enable access to topologically nontrivial properties. This observation of an unconventional superlattice structure establishes a powerful route for tailoring the tremendous array of magnetic and electronic behaviors hosted in related materials and may expand their use in low-power spintronic or topological quantum devices.}, author = {Fender, Shannon S. and Schnitzer, Noah and Fang, Wuzhang and Bhatt, Lopa and Huang, Dingbin and Malik, Amani and Gonzalez, Oscar and Sunko, Veronika and Xie, Lilia S. and Muller, David A. and Orenstein, Joseph and Ping, Yuan and Goodge, Berit H. and Bediako, D. Kwabena}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, number = {36}, pages = {32315--32320}, publisher = {American Chemical Society}, title = {{Unconventional superlattice ordering in intercalated transition metal dichalcogenide V1/3NbS2}}, doi = {10.1021/jacs.5c07385}, volume = {147}, year = {2025}, } @article{21433, abstract = {Altermagnets, magnetic materials with zero magnetization and spin-split band structure, have gained tremendous attention recently for their rich physics and potential applications. Here, we report on a microscopic tight-binding model that unveils a unique coupling between orbitals and spins in 𝑑-wave altermagnets, which gives rise to momentum-dependent and spin-selective optical absorption. This coupling promotes the controlled optical excitation of up or down spins depending on the polarization direction of linearly polarized light. Such an effect originates from the coupling of orbitals to the sublattice degree of freedom through the crystal field, which is then coupled to spins through the antiferromagnetic interaction. Our crystal field analysis, which is general to any type of altermagnet, helps understand the onset of altermagnetism from a microscopic point of view, and we use our results to propose clear magneto-optical signatures of our predictions. Our findings shine light on the interplay between orbitals and spins in altermagnets, thus paving the way towards novel orbitronic and optospintronic devices.}, author = {Vila, Marc and Sunko, Veronika and Moore, Joel E.}, issn = {2469-9969}, journal = {Physical Review B}, number = {2}, publisher = {American Physical Society}, title = {{Orbital-spin locking and its optical signatures in altermagnets}}, doi = {10.1103/bzzy-ngcs}, volume = {112}, year = {2025}, } @unpublished{21434, abstract = {Goldstone modes acquire a frequency gap in the presence of perturbations that break the underlying continuous symmetry. Here, we study the response of a spin-based Goldstone mode to strain and magnetic field in the broken helix, a multi-$\textbf{Q}$ phase of EuIn$_2$As$_2$. Optical polarimetry with spatial and temporal resolution allows us to access information about both the structure and frequency of optically excited spin-wave modes under different strain conditions. We observe nearly uniform spin precession characteristic of a Goldstone mode only when magnetic field dominates over strain. In this regime, the frequency depends linearly on the applied field. A symmetry analysis for predicting the mode frequency near zero field demonstrates that the observed scaling is of the lowest allowed order. This work thus demonstrates the connections between magnetic symmetries and the frequency dependence of the Goldstone mode in an external field, and illustrates the power of our technique for studying the dynamics of complex magnets.}, author = {Alex Liebman-Pelaez, Alex Liebman-Pelaez and Garratt, Samuel J. and Sunko, Veronika and Sun, Yue and Soh, Jian R. and Prabhakaran, Dharmalingam and Boothroyd, Andrew T. and Orenstein, Joseph}, booktitle = {arXiv}, title = {{Goldstone mode of the broken helix in U(1) magnet EuIn2As2}}, doi = {10.48550/arXiv.2501.09084}, year = {2025}, } @unpublished{21435, abstract = {Multiferroic materials, in which electric polarization and magnetic order coexist and couple, offer rich opportunities for both fundamental discovery and technology. However, multiferroicity remains rare due to conflicting electronic requirements for ferroelectricity and magnetism. One route to circumvent this challenge is to exploit the noncollinear ordering of spin cycloids, whose symmetry permits the emergence of polar order. In this work, we introduce another pathway to multiferroic order in which strain generates polarization in materials that host nonpolar spin spirals. To demonstrate this phenomenon, we chose the spin spiral in the well-studied helimagnet Cr1/3NbS2. To detect the induced polarization, we introduce the technique of magnetoelectric birefringence (MEB), an optical probe that enables spatially-resolved and unambiguous detection of polar order. By combining MEB imaging with strain engineering, we confirm the onset of a polar vector at the magnetic transition, establishing strained Cr1/3NbS2 as a type-II multiferroic.}, author = {Sun, Y. and Ahn, Y. and Sapkota, D. and Arachchige, H. S. and Xue, R. and Mozaffari, S. and Mandrus, D. G. and Zhao, L. and Orenstein, J. and Sunko, Veronika}, booktitle = {arXiv}, title = {{Strain-induced multiferroicity in Cr1/3NbS2}}, doi = {10.48550/arXiv.2510.11619}, year = {2025}, } @article{19809, abstract = {In many physical situations in which many-body assemblies exist at temperature T, a characteristic quantum-mechanical time scale of approximately h/kbT can be identified in both theory and experiment, leading to speculation that it may be the shortest meaningful time in such circumstances. This behavior can be investigated by probing the scattering rate of electrons in a broad class of materials often referred to as “strongly correlated metals”. It is clear that in some cases only electron–electron scattering can be its cause, while in others it arises from high-temperature scattering of electrons from quantized lattice vibrations, i.e., phonons. In metallic oxides, which are among the most studied materials, analysis of electrical transport does not satisfactorily identify the relevant scattering mechanism at “high” temperatures near room temperature. We therefore employ a contactless optical method to measure thermal diffusivity in two Ru-based layered perovskites, Sr3Ru2O7 and Sr2RuO4, and use the measurements to extract the dimensionless Lorenz ratio. By comparing our results to the literature data on both conventional and unconventional metals, we show how the analysis of high-temperature thermal transport can both give important insight into dominant scattering mechanisms and be offered as a stringent test of theories attempting to explain anomalous scattering.}, author = {Sun, Fei and Mishra, Simli and Stockert, Ulrike and Daou, Ramzy and Kikugawa, Naoki and Perry, Robin S. and Hassinger, Elena and Hartnoll, Sean A. and Mackenzie, Andrew P. and Sunko, Veronika}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, number = {35}, publisher = {National Academy of Sciences}, title = {{The Lorenz ratio as a guide to scattering contributions to transport in strongly correlated metals}}, doi = {10.1073/pnas.2318159121}, volume = {121}, year = {2024}, } @article{19816, abstract = {Understanding and manipulating emergent phases, which are themes at the forefront of quantum-materials research, rely on identifying their underlying symmetries. This general principle has been particularly prominent in materials with coupled electronic and magnetic degrees of freedom, in which magnetic order influences the electronic band structure and can lead to exotic topological effects. However, identifying symmetry of a magnetically ordered phase can pose a challenge, particularly in the presence of small domains. Here we introduce a multimodal approach for determining magnetic structures, which combines symmetry-sensitive optical probes, scattering, and group-theoretical analysis. We apply it to EuIn2⁢As2, a material that has received attention as a candidate axion insulator. While first-principles calculations predict this state on the assumption of a simple collinear antiferromagnetic structure, subsequent neutron-scattering measurements reveal a much more intricate magnetic ground state characterized by two coexisting magnetic wave vectors reached by successive thermal phase transitions. The proposed high- and low-temperature phases are a spin helix and a state with interpenetrating helical and Néel antiferromagnetic order termed a “broken helix,” respectively. Employing a multimodal approach, we identify the magnetic structure associated with these two phases of EuIn2⁢As2. We find that the higher-temperature phase is characterized by a variation of the magnetic moment amplitude from layer to layer, with the moment vanishing entirely in every third Eu layer. The lower-temperature structure is similar to the broken helix, with one important difference: Because of local strain, the relative orientation of the magnetic structure and the lattice is not fixed. Consequently, the symmetry required to protect the axion phase is not generically protected in EuIn2⁢As2, but we show that it can be restored if the magnetic structure is tuned with uniaxial strain. Finally, we present a spin Hamiltonian that identifies the spin interactions that account for the complex magnetic order in EuIn2⁢As2. Our work highlights the importance of a multimodal approach in determining the symmetry of complex order parameters.}, author = {Donoway, E. and Trevisan, T. V. and Liebman-Peláez, A. and Day, R. P. and Yamakawa, K. and Sun, Y. and Soh, J. R. and Prabhakaran, D. and Boothroyd, A. T. and Fernandes, R. M. and Analytis, J. G. and Moore, J. E. and Orenstein, J. and Sunko, Veronika}, issn = {2160-3308}, journal = {Physical Review X}, number = {3}, publisher = {American Physical Society}, title = {{Multimodal approach reveals the symmetry-breaking pathway to the broken helix in EuIn2As2}}, doi = {10.1103/physrevx.14.031013}, volume = {14}, year = {2024}, } @article{19803, abstract = {Eu⁢Cd2⁢P2 is notable for its unconventional transport: upon cooling the metallic resistivity changes slope and begins to increase, ultimately 100-fold, before returning to its metallic value. Surprisingly, this giant peak occurs at 18 K, well above the Néel temperature (𝑇𝑁) of 11.5 K. Using a suite of sensitive probes of magnetism, including resonant x-ray scattering and magneto-optical polarimetry, we have discovered that ferromagnetic order onsets above 𝑇𝑁 in the temperature range of the resistivity peak. The observation of inverted hysteresis in this regime shows that ferromagnetism is promoted by coupling of localized spins and itinerant carriers. The resulting carrier localization is confirmed by optical conductivity measurements.}, author = {Sunko, Veronika and Sun, Y. and Vranas, M. and Homes, C. C. and Lee, C. and Donoway, E. and Wang, Z.-C. and Balguri, S. and Mahendru, M. B. and Ruiz, A. and Gunn, B. and Basak, R. and Blanco-Canosa, S. and Schierle, E. and Weschke, E. and Tafti, F. and Frano, A. and Orenstein, J.}, issn = {2469-9969}, journal = {Physical Review B}, number = {14}, publisher = {American Physical Society}, title = {{Spin-carrier coupling induced ferromagnetism and giant resistivity peak in EuCd2P2}}, doi = {10.1103/physrevb.107.144404}, volume = {107}, year = {2023}, } @article{19821, abstract = {The adiabatic elastocaloric effect measures the temperature change of a given system with strain and provides a thermodynamic probe of the entropic landscape in the temperature-strain space. Here, we demonstrate that the DC bias strain-dependence of AC elastocaloric effect allows decomposition of the latter into symmetric (rotation-symmetry-preserving) and antisymmetric (rotation-symmetry-breaking) strain channels, using a tetragonal -electron intermetallic DyB2C2—whose antiferroquadrupolar order breaks local fourfold rotational symmetries while globally remaining tetragonal—as a showcase example. We capture the strain evolution of its quadrupolar and magnetic phase transitions using both singularities in the elastocaloric coefficient and its jumps at the transitions, and the latter we show follows a modified Ehrenfest relation. We find that antisymmetric strain couples to the underlying order parameter in a biquadratic (linear-quadratic) manner in the antiferroquadrupolar (canted antiferromagnetic) phase, which are attributed to a preserved (broken) global tetragonal symmetry, respectively. The broken tetragonal symmetry in the magnetic phase is further evidenced by elastocaloric strain-hysteresis and optical birefringence. Additionally, within the staggered quadrupolar order, the observed elastocaloric response reflects a quadratic increase of entropy with antisymmetric strain, analogous to the role magnetic field plays for Ising antiferromagnetic orders by promoting pseudospin flips. Our results demonstrate AC elastocaloric effect as a compact and incisive thermodynamic probe into the coupling between electronic degrees of freedom and strain in free energy, which holds the potential for investigating and understanding the symmetry of a wide variety of ordered phases in broader classes of quantum materials.}, author = {Ye, Linda and Sun, Yue and Sunko, Veronika and Rodriguez-Nieva, Joaquin F. and Ikeda, Matthias S. and Worasaran, Thanapat and Sorensen, Matthew E. and Bachmann, Maja D. and Orenstein, Joseph and Fisher, Ian R.}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, number = {35}, publisher = {National Academy of Sciences}, title = {{Elastocaloric signatures of symmetric and antisymmetric strain-tuning of quadrupolar and magnetic phases in DyB2C2}}, doi = {10.1073/pnas.2302800120}, volume = {120}, year = {2023}, } @article{19828, abstract = {We describe an optical method to directly measure the position-dependent thermal diffusivity of reflective single crystal samples across a broad range of temperatures for condensed matter physics research. Two laser beams are used, one as a source to locally modulate the sample temperature, and the other as a probe of sample reflectivity, which is a function of the modulated temperature. Thermal diffusivity is obtained from the phase delay between source and probe signals. We combine this technique with a microscope setup in an optical cryostat, in which the sample is placed on a three-axis piezo-stage, allowing for spatially resolved measurements. Furthermore, we demonstrate experimentally and mathematically that isotropic in-plane diffusivity can be obtained when overlapping the two laser beams instead of separating them in the traditional way, which further enhances the spatial resolution to a micron scale, especially valuable when studying inhomogeneous or multidomain samples. We discuss in detail the experimental conditions under which this technique is valuable and demonstrate its performance on two stoichiometric bilayer ruthenates: Sr3Ru2O7 and Ca3Ru2O7. The spatial resolution allowed us to study the diffusivity in single domains of the latter, and we uncovered a temperature-dependent in-plane diffusivity anisotropy. Finally, we used the enhanced spatial resolution enabled by overlapping the two beams to measure the temperature-dependent diffusivity of Ti-doped Ca3Ru2O7, which exhibits a metal–insulator transition. We observed large variations of transition temperature over the same sample, originating from doping inhomogeneity and pointing to the power of spatially resolved techniques in accessing inherent properties.}, author = {Sun, F. and Mishra, S. and McGuinness, P. H. and Filipiak, Z. H. and Marković, I. and Sokolov, D. A. and Kikugawa, N. and Orenstein, J. W. and Hartnoll, S. A. and Mackenzie, A. P. and Sunko, Veronika}, issn = {1089-7623}, journal = {Review of Scientific Instruments}, number = {4}, publisher = {AIP Publishing}, title = {{A spatially resolved optical method to measure thermal diffusivity}}, doi = {10.1063/5.0098800}, volume = {94}, year = {2023}, } @article{19822, abstract = {>Controlling spin wave excitations in magnetic materials underpins the burgeoning field of magnonics. Yet, little is known about how magnons interact with the conduction electrons of itinerant magnets, or how this interplay can be controlled. Via a surface-sensitive spectroscopic approach, we demonstrate a strong electron–magnon coupling at the Pd-terminated surface of the delafossite oxide PdCoO2, where a polar surface charge mediates a Stoner transition to itinerant surface ferromagnetism. We show how the coupling is enhanced sevenfold with increasing surface disorder, and concomitant charge carrier doping, becoming sufficiently strong to drive the system into a polaronic regime, accompanied by a significant quasiparticle mass enhancement. Our study thus sheds light on electron–magnon interactions in solid-state materials, and the ways in which these can be controlled.}, author = {Mazzola, F. and Yim, C. -M. and Sunko, Veronika and Khim, S. and Kushwaha, P. and Clark, O. J. and Bawden, L. and Marković, I. and Chakraborti, D. and Kim, T. K. and Hoesch, M. and Mackenzie, A. P. and Wahl, P. and King, P. D. C.}, issn = {2397-4648}, journal = {npj Quantum Materials}, publisher = {Springer Nature}, title = {{Tuneable electron–magnon coupling of ferromagnetic surface states in PdCoO2}}, doi = {10.1038/s41535-022-00428-8}, volume = {7}, year = {2022}, } @article{19807, abstract = {Microstructures can be carefully designed to reveal the quantum phase of the wave-like nature of electrons in a metal. Here, we report phase-coherent oscillations of out-of-plane magnetoresistance in the layered delafossites PdCoO2 and PtCoO2. The oscillation period is equivalent to that determined by the magnetic flux quantum, h/e, threading an area defined by the atomic interlayer separation and the sample width, where h is Planck’s constant and e is the charge of an electron. The phase of the electron wave function appears robust over length scales exceeding 10 micrometers and persisting up to temperatures of T > 50 kelvin. We show that the experimental signal stems from a periodic field modulation of the out-of-plane hopping. These results demonstrate extraordinary single-particle quantum coherence lengths in delafossites.}, author = {Putzke, Carsten and Bachmann, Maja D. and McGuinness, Philippa and Zhakina, Elina and Sunko, Veronika and Konczykowski, Marcin and Oka, Takashi and Moessner, Roderich and Stern, Ady and König, Markus and Khim, Seunghyun and Mackenzie, Andrew P. and Moll, Philip J.W.}, issn = {1095-9203}, journal = {Science}, number = {6496}, pages = {1234--1238}, publisher = {American Association for the Advancement of Science}, title = {{h/e oscillations in interlayer transport of delafossites}}, doi = {10.1126/science.aay8413}, volume = {368}, year = {2020}, } @article{19812, abstract = {A nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO2, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an “intertwined” excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO2 as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials.}, author = {Sunko, Veronika and Mazzola, F. and Kitamura, S. and Khim, S. and Kushwaha, P. and Clark, O. J. and Watson, M. D. and Marković, I. and Biswas, D. and Pourovskii, L. and Kim, T. K. and Lee, T.-L. and Thakur, P. K. and Rosner, H. and Georges, A. and Moessner, R. and Oka, T. and Mackenzie, A. P. and King, P. D. C.}, issn = {2375-2548}, journal = {Science Advances}, number = {6}, publisher = {American Association for the Advancement of Science}, title = {{Probing spin correlations using angle-resolved photoemission in a coupled metallic/Mott insulator system}}, doi = {10.1126/sciadv.aaz0611}, volume = {6}, year = {2020}, }