We present evidence for quantum oscillations in the pressure-induced metallic state of the 4$d$ layered perovskite Ca$_2$RuO$_4$. A complicated oscillation spectrum is observed, which is both temperature and field dependent, with unusually light cyclotron masses in the range of $m^*/m_e$ $\sim$ 0.6 -- 3, suggesting that the pressure-induced metallic state is a weakly correlated Fermi liquid. We compare our observations to band structure calculations within the local spin density approximation, and conclude that some features of the spectrum are a result of non-linear spin splitting effects.
We investigate the dynamical properties of Sr$_2$RuO$_4$ at zero and very low temperature using density functional theory plus dynamical mean-field theory with an exact diagonalization solver. By considering rotationally invariant local interaction, we examine how Hund's coupling and spin-orbit coupling affect the correlated nature of the system. In the absence of Hund's coupling, the system shows a Fermi liquid behavior over the entire range of temperatures we consider. We confirm that the Fermi liquid persists at zero temperature even with nonzero Hund's coupling; however, at sufficient temp…
Localization in ruthenates: magnetic and electronic properties of Ca(2-x)Sr(x)RuO(4)
用LDA、LDA+U和动力学平均场近似方法计算了Ca（2-x）Sr（x）RuO（4）（0<= x <= 2）金属相和绝缘相的电子结构。当x=0时，基态是轨道非简并的反铁磁绝缘体。当0.2<x 0.5时<0.5 we propose a state with partial orbital and spin ordering. For x>，所观察到的居里-外斯顺磁金属态具有一个非预期自旋S=1/2的局域磁矩，这可以用三个Ru-4d轨道中只有两个的局域化来解释。
We show that spin-orbit coupling (SOC) plays Janus-faced roles on the orbitally-selective Mott transitions in a three-orbital Hubbard model with crystal field splitting at a specific filling of $2/3$, which is a minimal Hamiltonian for ruthenates. While the SOC favors metallic state due to enhancement of orbital hybridization at smaller on-site Coulomb repulsions, it stabilizes the Mott insulating state ascribed to lifting of orbital degeneracies and enhancement of band polarizations at larger electronic interaction. Moreover, an orbitally-selective non-Fermi liquid (OSnFL), where breakdown an…
We measure the Shubnikov-de Haas effect in thin-film Sr$_2$RuO$_4$ grown on an (LaAlO$_3$)$_{0.29}$-(SrAl$_{1/2}$Ta$_{1/2}$O$_3$)$_{0.71}$ (LSAT) substrate. We detect all three known Fermi surfaces and extract the Fermi surface volumes, cyclotron effective masses, and quantum lifetimes. We show that the electronic structure is nearly identical to that of single-crystal Sr$_2$RuO$_4$, and that the quasiparticle lifetime is consistent with the Tc of comparably clean, single-crystal Sr$_2$RuO$_4$. Unlike single-crystal Sr$_2$RuO$_4$, where the quantum and transport lifetimes are roughly equal, we…
Combining quasistatic and time-resolved transport measurements with X-ray and neutron diffraction experiments we study the non-equilibrium states that arise in pure and in Ti substituted Ca$_2$RuO$_4$ under the application of current densities. Time-resolved studies of the current-induced switching find a slow conductance relaxation that can be identified with heating and a fast one that unambiguously proves an intrinsic mechanism. The current-induced phase transition leads to complex diffraction patterns. Separated Bragg reflections that can be associated with the metallic and insulating phas…
We present a general methodology that enables the disentanglement of the electronic and lattice contributions to the metal-insulator transition by building an energy landscape from numerical solutions of the equation of state. The methodology works with any electronic structure method that provides electronic expectation values at given atomic positions. Applying the theory to rare-earth perovskite nickelates ($R$NiO$_3$) and Ruddlesden-Popper calcium ruthenates (Ca$_2$RuO$_4$) in bulk, heterostructure and epitaxially strained thin film forms using equation of state results from density functi…
Orbital and spin correlations in Ca$_{2-x}$Sr$_x$RuO$_4$: A mean field study
合金Ca $_{2-x}$ Sr $_x$ RuO $_4$具有复杂的相图，具有特殊的磁性金属相。在本文中，这种合金的一些方面进行了讨论的基础上的平均场理论的一个有效的Kugel-Khomskii模型的本地化轨道和自旋自由度。这个模型的结果从轨道选择性莫特跃迁，在三带系统本地化的两个轨道，而离开第三个巡回。特别注意的是周围的区域的结构量子相变在$ x \approx 0.5 $的晶格变化从四方晶系正交对称，而离开系统的金属。这种转变产生了从铁磁到反铁磁自旋相关的变化。给出了该跃迁的完整平均场相图，包括轨道和自旋序。自旋磁化率的各向异性是自旋轨道耦合和轨道关联的结果，是这些阶段之一的一个标志。在占主导地位的反铁磁相，我们描述了在磁场的变磁过渡，并表明耦合的巡回带的本地化的自由度产生一个异常的纵向磁阻过渡。这两种现象都与外部磁场中铁磁和反铁磁畴的演化有关，并与实验结果定性一致。
We investigate the role of electron correlation in the electronic structure of honeycomb lattice Li$_2$RuO$_3$ using photoemission spectroscopy and band structure calculations. Monoclinic Li$_2$RuO$_3$ having Ru network as honeycomb lattice undergoes magneto-structural transition at T$_c$ $\sim$ 540 K from high temperature phase $C2/m$ to low temperature dimerized phase $P2_1/m$. Room temperature valence band photoemission spectra reveal an insulating ground state with no intensity at Fermi level ($E_F$). Ru 4$d$ band extracted from high and low photon energy valence band photoemission spectra…
Sr$_2$RuO$_4$, like doped cuprates and barium bismuthate, is a negative charge-transfer gap even parity superconductor with $\frac{3}{4}$-filled oxygen band
Sr $_2$ RuO $_4$中超导性的综合理论必须解释那些提出偶宇称超导序的实验和其他提出破缺时间反演对称性的实验。完整性进一步要求该理论适用于Ca $_2$ RuO $_4$，这是一种莫特-哈伯德半导体，它表现出前所未有的绝缘体到金属转变，由非常小的电场驱动，并且还通过掺杂非常小的电子浓度，导致接近铁磁性的金属态。将以前提出的超导铜酸盐[Phys. Rev. B { \bf 98}，205153]的价态跃迁模型推广到Sr $_2$ RuO $_4$和Ca $_2$ RuO $_4$。从绝缘体到金属的转变与Mott-Hubbard半导体的简单熔化所预期的不同。相反，Ru离子在半导体中以低自旋Ru $^{4+}$的形式出现，在金属中以高自旋Ru $^{3+}$的形式出现，价态跃迁背后的驱动力是强自旋-电荷耦合和由此产生的低电荷态下的大电离能。金属和超导的钌酸盐是双组分系统，其中半填充的高自旋Ru $^{3+}$离子决定磁行为，但不决定输运，而电荷载流子完全在层氧离子上，其具有平均电荷-1.5。自旋单线态超导性仅从层氧离子的相关晶格受抑3/4填充带演化而来，这与量子多体计算一致，量子多体计算已经证明了超导对-对相关性的电子-电子相互作用的增强唯一地在该填充处或非常接近该填充处[Phys. Rev. B { \bf 93}，165110和{ \bf 93}，205111]。几个模型具…
Quantum Oscillations of $\mathrm{Sr}_2\mathrm{RuO}_4$ under c-Axis Uniaxial Stress
Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews（圣安德鲁斯大学物理与天文学学院苏格兰大学物理联盟）；National Institute for Materials Science（国立材料研究所）；Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院量子材料与技术研究所）
T-square electric resistivity and its thermal counterpart in RuO$_2$
Laboratoire de Physique et d’Etude des Matériaux (CNRS) ESPCI Paris, PSL Université（巴黎高等物理化工学院，巴黎文理研究大学）；Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology（华中科技大学物理学院，武汉国家强磁场中心）；Laboratoire de Cristallographie et Sciences des Matériaux, Université de Caen Normandie, ENSICAEN, CNRS, Normandie Univ, CRISMAT UMR6508（卡昂诺曼底大学）；Nantes Université, CNRS, Institut des Matériaux de Nantes Jean Rouxel (IMN)-UMR 6502（南特大学）
Insulating transport in anisotropic metals: breakdown of Drude transport and the puzzling $c$-axis resistivity of Sr$_2$RuO$_4$ and other layered oxides
Correlation-driven tunability of altermagnetism in RuO$_2$
Center for Computational Quantum Physics (CCQ), Flatiron Institute（计算量子物理中心（CCQ），平顿研究所）；Institute of Solid State Physics, TU Wien（固体的物理学研究所，维也纳工业大学）；Theoretical Division, Los Alamos National Laboratory（理论部，洛斯阿拉莫斯国家实验室）；POSCO Holdings（POSCO控股）；Institute for Data Innovation in Science, Seoul National University（科学数据创新研究所，首尔大学）；Department of Materials Science and Engineering, Kyung Hee University（材料科学与工程系，庆熙大学）
The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB$_6$ and subsequently YbB$_{12}$ is a subject of intense inquiry. Here we shed light on this question by comparing quantum oscillations between the high magnetic field-induced metallic regime in YbB$_{12}$ and the unconventional insulating regime. In the field-induced metallic regime beyond 47 T, we find prominent quantum oscillations in the contactless resistivity characterised by multiple frequencies up to at least 3000 T and heavy effective masses up to at least 17 $m_\te…
Electrical Transport and Quantum Oscillations in the Metallic Spin Supersolid EuCo2Al9
Hefei Institutes of Physical Science, Chinese Academy of Sciences（中国科学院合肥物质科学研究院）；University of Science and Technology of China（中国科学技术大学）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；China Jiliang University（中国计量大学）；Shanghai Jiao Tong University（上海交通大学）；Nanjing University（南京大学）
VO2, of interest for decades due to both its phenomenology and its potential applications, has a monoclinic distortion of the rutile crystal structure at ambient temperature that is coupled to its metal-insulator transition (MIT). In contrast, RuO2 has three electrons more per formula unit, is a metallic conductor, and has an undistorted rutile structure. Here we report a systematic study of Ru-doped VO2 (V1-xRuxO2); generally characterizing its crystal structure, magnetic and electronic properties, and heat capacity. The composition-dependent Wilson ratio is determined. We find that an unusua…
A new layered perovskite-type oxide Ba$_2$RhO$_4$ was synthesized by a high-pressure technique with the support of convex-hull calculations. The crystal and electronic structure were studied by both experimental and computational tools. Structural refinements for powder x-ray diffraction data showed that Ba$_2$RhO$_4$ crystallizes in a K$_2$NiF$_4$-type structure, isostructural to Sr$_2$RuO$_4$ and Ba$_2$IrO$_4$. Magnetic, resistivity, and specific heat measurements for polycrystalline samples of Ba$_2$RhO$_4$ indicate that the system can be characterized as a correlated metal. Despite the clo…
Shubnikov-de Haas oscillations from topological surface states of metallic Bi$_2$Se$_{2.1}$Te$_{0.9}$
研究了p型金属Bi $_2$ Se $_{2.1}$ Te $_{0.9}$电导率的量子振荡。的依赖关系的振荡的角度上的磁场与表面以及确定的Berry相位从朗道水平风扇图表明，所观察到的振荡产生的表面载流子的特性狄拉克色散。表征表面导电的几个量计算采用Lifshitz-Kosevich理论。相对于狄拉克点的费米能的低值与体空穴载流子的金属特性是一致的。我们的结论是，由于特殊的形状的价带，Shubnikov-de Haas振荡的散装载流子被转移到更高的磁场，这允许检测的量子振荡的拓扑表面态在较低的字段。
Within condensed-matter systems, strong electronic interactions often lead to exotic quantum phases. A recent manifestation of this is the unexpected observation of magnetic quantum oscillations and metallic thermal transport, both properties of systems with Fermi surfaces of itinerant quasiparticles, in the Kondo insulators SmB6 and YbB$_{12}$. To understand these phenomena, it is informative to study their evolution as the energy gap of the Kondo-Insulator state is closed by a large magnetic field. We show here that both the quantum-oscillation frequency and the cyclotron mass display a stro…
We show that a static electric field induces the transition from a ferromagnetic metal to an antiferromagnetic insulator owing to the Bloch oscillation of conduction electrons. In the steady state, the electric current is inversely proportional to the applied electric field, implying the nonperturbative insulating nature that is different from the Wannier-Stark localization. Possible experimental realization based on recent terahertz pulse sources is discussed.
We provide a complete theoretical interpretation of the metallic broken spin/valley symmetry states recently discovered in ABC trilayer graphene (ABC) perturbed by a large transverse displacement field. Our conclusions combine insights from ABC trilayer graphene electronic structure models and mean field theory, and are guided by precise magneto-oscillation Fermi-surface-area measurements. We conclude that the physics of ABC trilayer graphene is shaped by the principle of momentum-space condensation, which favors Fermi surface reconstructions enabled by broken spin/valley flavor symmetries whe…
