@article{19811, abstract = {We report on a combined study of the de Haas-van Alphen effect and angle-resolved photoemission spectroscopy on single crystals of the metallic delafossite rounded off by ab initio band structure calculations. A high-sensitivity torque magnetometry setup with superconducting quantum interference device readout and synchrotron-based photoemission with a light spot size of enabled high-resolution data to be obtained from samples as small as . The Fermi surface shape is nearly cylindrical with a rounded hexagonal cross section enclosing a Luttinger volume of 1.00(1) electrons per formula unit.}, author = {Arnold, F. and Naumann, M. and Khim, S. and Rosner, H. and Sunko, Veronika and Mazzola, F. and King, P. D. C. and Mackenzie, A. P. and Hassinger, E.}, issn = {2469-9969}, journal = {Physical Review B}, number = {7}, publisher = {American Physical Society}, title = {{Quasi-two-dimensional Fermi surface topography of the delafossite PdRhO2}}, doi = {10.1103/physrevb.96.075163}, volume = {96}, year = {2017}, } @article{834, abstract = {Thermal and many-body localized phases are separated by a dynamical phase transition of a new kind. We analyze the distribution of off-diagonal matrix elements of local operators across this transition in two different models of disordered spin chains. We show that the behavior of matrix elements can be used to characterize the breakdown of thermalization and to extract the many-body Thouless energy. We find that upon increasing the disorder strength the system enters a critical region around the many-body localization transition. The properties of the system in this region are: (i) the Thouless energy becomes smaller than the level spacing, (ii) the matrix elements show critical dependence on the energy difference, and (iii) the matrix elements, viewed as amplitudes of a fictitious wave function, exhibit strong multifractality. This critical region decreases with the system size, which we interpret as evidence for a diverging correlation length at the many-body localization transition. Our findings show that the correlation length becomes larger than the accessible system sizes in a broad range of disorder strength values and shed light on the critical behavior near the many-body localization transition.}, author = {Serbyn, Maksym and Zlatko, Papic and Abanin, Dmitry}, issn = {2469-9950}, journal = {Physical Review B - Condensed Matter and Materials Physics}, number = {10}, publisher = {American Physical Society}, title = {{Thouless energy and multifractality across the many-body localization transition}}, doi = {10.1103/PhysRevB.96.104201}, volume = {96}, year = {2017}, } @article{9065, abstract = {Magnetic anisotropy in strontium iridate (Sr2IrO4) is found to be large because of the strong spin-orbit interactions. In our work, we studied the in-plane magnetic anisotropy of Sr2IrO4 and traced the anisotropic exchange interactions between the isospins in the crystal. The magnetic-field-dependent torque τ(H) showed a prominent transition from the canted antiferromagnetic state to the weak ferromagnetic (WFM) state. A comprehensive analysis was conducted to examine the isotropic and anisotropic regimes and probe the easy magnetization axis along the a b plane. The angle-dependent torque τ(θ) revealed a deviation from the sinusoidal behavior, and small differences in hysteresis were observed around 0° and 90° in the low-magnetic-field regime. This indicates that the orientation of the easy axis of the FM component is along the b axis, where the antiferromagnetic to WFM spin-flop transition occurs. We compared the coefficients of the magnetic susceptibility tensors and captured the anisotropy of the material. The in-plane τ(θ) revealed a tendency toward isotropic behavior for fields with values above the field value of the WFM transition.}, author = {Nauman, Muhammad and Hong, Yunjeong and Hussain, Tayyaba and Seo, M. S. and Park, S. Y. and Lee, N. and Choi, Y. J. and Kang, Woun and Jo, Younjung}, issn = {2469-9950}, journal = {Physical Review B}, number = {15}, publisher = {American Physical Society}, title = {{In-plane magnetic anisotropy in strontium iridate Sr2IrO4}}, doi = {10.1103/physrevb.96.155102}, volume = {96}, year = {2017}, } @article{7065, abstract = {Magneto-quantum oscillation experiments in high-temperature superconductors show a strong thermally induced suppression of the oscillation amplitude approaching the critical dopings [B. J. Ramshaw et al., Science 348, 317 (2014); H. Shishido et al., Phys. Rev. Lett. 104, 057008 (2010); P. Walmsley et al., Phys. Rev. Lett. 110, 257002 (2013)]—in support of a quantum-critical origin of their phase diagrams. We suggest that, in addition to a thermodynamic mass enhancement, these experiments may directly indicate the increasing role of quantum fluctuations that suppress the quantum oscillation amplitude through inelastic scattering. We show that the traditional theoretical approaches beyond Lifshitz-Kosevich to calculate the oscillation amplitude in correlated metals result in a contradiction with the third law of thermodynamics and suggest a way to rectify this problem.}, author = {Shekhter, Arkady and Modic, Kimberly A and McDonald, R. D. and Ramshaw, B. J.}, issn = {2469-9969}, journal = {Physical Review B}, number = {12}, publisher = {APS}, title = {{Thermodynamic constraints on the amplitude of quantum oscillations}}, doi = {10.1103/physrevb.95.121106}, volume = {95}, year = {2017}, } @article{724, abstract = {We investigate the stationary and dynamical behavior of an Anderson localized chain coupled to a single central bound state. Although this coupling partially dilutes the Anderson localized peaks towards nearly resonant sites, the most weight of the original peaks remains unchanged. This leads to multifractal wave functions with a frozen spectrum of fractal dimensions, which is characteristic for localized phases in models with power-law hopping. Using a perturbative approach we identify two different dynamical regimes. At weak couplings to the central site, the transport of particles and information is logarithmic in time, a feature usually attributed to many-body localization. We connect such transport to the persistence of the Poisson statistics of level spacings in parts of the spectrum. In contrast, at stronger couplings the level repulsion is established in the entire spectrum, the problem can be mapped to the Fano resonance, and the transport is ballistic.}, author = {Hetterich, Daniel and Serbyn, Maksym and Domínguez, Fernando and Pollmann, Frank and Trauzettel, Björn}, issn = {2469-9950}, journal = {Physical Review B}, number = {10}, publisher = {American Physical Society}, title = {{Noninteracting central site model localization and logarithmic entanglement growth}}, doi = {10.1103/PhysRevB.96.104203}, volume = {96}, year = {2017}, } @article{995, abstract = {Recently it was shown that an impurity exchanging orbital angular momentum with a surrounding bath can be described in terms of the angulon quasiparticle [Phys. Rev. Lett. 118, 095301 (2017)]. The angulon consists of a quantum rotor dressed by a many-particle field of boson excitations, and can be formed out of, for example, a molecule or a nonspherical atom in superfluid helium, or out of an electron coupled to lattice phonons or a Bose condensate. Here we develop an approach to the angulon based on the path-integral formalism, which sets the ground for a systematic, perturbative treatment of the angulon problem. The resulting perturbation series can be interpreted in terms of Feynman diagrams, from which, in turn, one can derive a set of diagrammatic rules. These rules extend the machinery of the graphical theory of angular momentum - well known from theoretical atomic spectroscopy - to the case where an environment with an infinite number of degrees of freedom is present. In particular, we show that each diagram can be interpreted as a 'skeleton', which enforces angular momentum conservation, dressed by an additional many-body contribution. This connection between the angulon theory and the graphical theory of angular momentum is particularly important as it allows to systematically and substantially simplify the analytical representation of each diagram. In order to exemplify the technique, we calculate the 1- and 2-loop contributions to the angulon self-energy, the spectral function, and the quasiparticle weight. The diagrammatic theory we develop paves the way to investigate next-to-leading order quantities in a more compact way compared to the variational approaches.}, author = {Bighin, Giacomo and Lemeshko, Mikhail}, issn = {2469-9950}, journal = {Physical Review B - Condensed Matter and Materials Physics}, number = {8}, publisher = {American Physical Society}, title = {{Diagrammatic approach to orbital quantum impurities interacting with a many-particle environment}}, doi = {10.1103/PhysRevB.96.085410}, volume = {96}, year = {2017}, } @article{986, abstract = {The many-body localization transition (MBLT) between ergodic and many-body localized phases in disordered interacting systems is a subject of much recent interest. The statistics of eigenenergies is known to be a powerful probe of crossovers between ergodic and integrable systems in simpler examples of quantum chaos. We consider the evolution of the spectral statistics across the MBLT, starting with mapping to a Brownian motion process that analytically relates the spectral properties to the statistics of matrix elements. We demonstrate that the flow from Wigner-Dyson to Poisson statistics is a two-stage process. First, a fractal enhancement of matrix elements upon approaching the MBLT from the delocalized side produces an effective power-law interaction between energy levels, and leads to a plasma model for level statistics. At the second stage, the gas of eigenvalues has local interactions and the level statistics belongs to a semi-Poisson universality class. We verify our findings numerically on the XXZ spin chain. We provide a microscopic understanding of the level statistics across the MBLT and discuss implications for the transition that are strong constraints on possible theories.}, author = {Serbyn, Maksym and Moore, Joel}, issn = {2469-9969}, journal = {Physical Review B - Condensed Matter and Materials Physics}, number = {4}, publisher = {American Physical Society}, title = {{Spectral statistics across the many-body localization transition}}, doi = {10.1103/PhysRevB.93.041424}, volume = {93}, year = {2016}, } @article{987, abstract = {In contrast to bulk FeSe, which exhibits nematic order and low temperature superconductivity, highly doped FeSe reverses the situation, having high temperature superconductivity appearing alongside a suppression of nematic order. To investigate this phenomenon, we study a minimal electronic model of FeSe, with interactions that enhance nematic fluctuations. This model is sign problem free, and is simulated using determinant quantum Monte Carlo (DQMC). We developed a DQMC algorithm with parallel tempering, which proves to be an efficient source of global updates and allows us to access the region of strong interactions. Over a wide range of intermediate couplings, we observe superconductivity with an extended s-wave order parameter, along with enhanced, but short-ranged, q=(0,0) ferro-orbital (nematic) order. These results are consistent with approximate weak-coupling treatments that predict that nematic fluctuations lead to superconducting pairing. Surprisingly, in the parameter range under study, we do not observe nematic long-range order. Instead, at stronger coupling an unusual insulating phase with q=(π,π) antiferro-orbital order appears, which is missed by weak-coupling approximations.}, author = {Dumitrescu, Philipp and Serbyn, Maksym and Scalettar, Richard and Vishwanath, Ashvin}, issn = {2469-9969}, journal = {Physical Review B}, number = {15}, publisher = {American Physical Society}, title = {{Superconductivity and nematic fluctuations in a model of doped FeSe monolayers: Determinant quantum Monte Carlo study}}, doi = {10.1103/PhysRevB.94.155127}, volume = {94}, year = {2016}, }