The low-energy electronic structure of the itinerant metamagnet Sr3Ru2O7 is investigated by angle resolved photoemission and density functional calculations. We find well-defined quasiparticle bands with resolution limited line widths and Fermi velocities up to an order of magnitude lower than in single layer Sr2RuO4. The complete topography, the cyclotron masses and the orbital character of the Fermi surface are determined, in agreement with bulk sensitive de Haas - van Alphen measurements. An analysis of the dxy band dispersion reveals a complex density of states including van Hove singularities (vHs) near the Fermi level; a situation which is favorable for magnetic instabilities.
It is shown that metamagnetic transition in metals can occur via the formation of electronic nematic order. We consider a simple model where the spin-dependent Fermi surface instability gives rise to the formation of an electronic nematic phase upon increasing the applied Zeeman magnetic field. This leads to two consecutive metamagnetic transitions that separate the nematic phase from the low-field and high-field 'isotropic' metallic phases. Possible connection to the physics of the bilayer Ruthenate, Sr$_3$Ru$_2$O$_7$, is also discussed.
We report, for the first time, measurements of the third order, $χ_3$ and fifth order, $χ_5$, susceptibilities in an itinerant oxide metamagnet, Sr$_3$Ru$_2$O$_7$ for magnetic fields both parallel and perpendicular to the c-axis. These susceptibilities exhibit maxima in their temperature dependence such that $T_1 \approx 2T_3 \approx 4T_5$ where the $T_i$ are the position in temperature where a peak in the $i$-th order susceptibility occurs. These features taken together with the scaling of the critical field with the temperature $T_1$ observed in a diverse variety of itinerant metamagnets fin…
Critical thermodynamics close to a metamagnetic quantum critical endpoint (QCEP) in a metal is discussed within the framework of spin-fluctuation theory. We analyze the effective potential for the Ising order parameter that is renormalized by spin-fluctuations and acquires a characteristic temperature dependence. The resulting magnetic field, H, and temperature, T, dependence of the magnetization, specific heat, thermal expansion, magnetostriction, susceptibility and the Grüneisen parameter are determined, and the crossover lines in the (H,T) phase diagram are specified. We point out that the …
We have investigated the spin dynamics in the bilayered perovskite Sr3Ru2O7 as a function of magnetic field and temperature using 17O-NMR. This system sits close to a metamagnetic quantum critical point (MMQCP) for the field perpendicular to the ruthenium oxide planes. We confirm Fermi-liquid behavior at low temperatures except for a narrow field region close to the MMQCP. The nuclear spin-lattice relaxation rate divided by temperature 1/T1T is enhanced on approaching the metamagnetic critical field of 7.9 T and at the critical field 1/T1T continues to increase and does not show Fermi- liquid …
Itinerant metamagnetism transition is observed and studied in perovskite La1-xCaxMn0.90Cu0.10O3 system for x = 0.30. At a constant low temperature, 10 K < T < 150 K, there is a continuous second-order metamagnetism jump from a low magnetic state to a high one with the magnetic field H increasing. However, at an exceeding low temperature, T = 2.5 K, the metamagnetism jump at H = 3.5 T becomes to be a robust first-order transition, and another metamagnetism transition occurs at a higher field H = 7.0 T. Since there is no charge ordering sign in the present system, it can not be understood by usi…
Focus is given on the macroscopic and microscopic experimental works realized during a decade on the clear case of itinerant metamagnetism in the heavy fermion paramagnetic compound CeRu2Si2 . Emphasis is made on the feedback between the band structure, the exchange coupling and the lattice instability. Sweeps in magnetic field, pressure and temperature feel the pseudogap of this strongly correlated electronic system as well as its equivalent CeRu2Ge2 at a fictitious negative pressure. Some mysteries persist as the complete observation of the FS above the metamagnetic field HM and the detectio…
We performed nuclear-magnetic-resonance (NMR) measurements on itinerant-electron metamagnet UCoAl in order to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization $M_c$ and its fluctuation $S_c$ from the measurements of Knight shift and nuclear spin-lattice relaxation rate $1/T_1$ as a function of the c-axis external field ($H_c$) and temperature ($T$). We developed contour plots of $M_c$ and $S_c$ on the $H_c$ - $T$ phase diagram, and observed the strong divergence of $S_c$ at the CEP. The critical exponents of $M…
Triple-layered ruthenate Sr$_4$Ru$_3$O$_{10}$ shows a first-order itinerant metamagnetic transition for in-plane magnetic fields. Our experiments revealed rather surprising behavior in the low-temperature transport properties near this transition. The in-plane magnetoresistivity $ρ$$_{ab}$(H) exhibits ultrasharp steps as the magnetic field sweeps down through the transition. Temperature sweeps of $ρ$$_{ab}$ for fields within the transition regime show non-metallic behavior in the up-sweep cycle of magnetic field, but show a significant drop in the down-sweep cycle. These observations indicate …
We report a uniaxial-pressure study on the magnetisation of single crystals of the bilayer perovskite Sr3Ru2O7, a metamagnet close to a ferromagnetic instability. We observed that the application of a uniaxial pressure parallel to the c-axis induces ferromagnetic ordering with a Curie temperature of about 80 K and critical pressures of about 4 kbar or higher. This value for the critical pressure is even higher than the value previously reported (~ 1 kbar), which might be attributed to the difference of the impurity level. Below the critical pressure parallel to the c-axis, the metamagnetic fie…
We report the results of a study of the di erential magnetic susceptibility of Sr3Ru2O7 as a function of temperature and magnetic elds applied at a series of angles to the ab plane. By analysing the real and imaginary parts of the susceptibility, we conclude that the eld angle acts as a continuous tuning parameter for the critical end-point to a line of rst order metamagnetic phase transitions. The end-point sits at approximately 1.25K for elds applied in the ab plane, and is depressed to below 50 mK when the eld is aligned within 10 of the c axis.
An investigation of La and Ca doped Sr4Ru3O10, featuring a coexistence of interlayer ferromagnetism and intralayer metamagnetism, is presented. La doping readily changes magnetism between ferromagnetism and metamagnetism by tuning the density of states. It also results in different Curie temperatures for the c-axis and the basal plane, highlighting a rare spin-orbit coupling with the crystal field states. In contrast, Ca doping enhances the c-axis ferromagnetism and the magnetic anisotropy. La doping also induces a dimensional crossover in the interlayer transport whereas Ca doping exhibits a …
It is known that itinerant metamagnetic transitions can be driven by features in the electronic density of states. We study the signatures of these transitions in the entropy and specific heat for a variety of different cases, identifying the key features which differ from naive expectations, such as enhanced critical fields and non-Fermi liquid temperature dependencies. We begin with the generic case of a logarithmically divergent density of states, as caused by a two dimensional van Hove singularity. We then study a specific model for the bandstructure of Sr3Ru2O7, a material with a well-stu…
We examine the effects of long-range dipolar forces on metamagnetic transitions and generalize the theory of Condon domains to the case of an itinerant electron system undergoing a first-order metamagnetic transition. We demonstrate that within a finite range of the applied field, dipolar interactions induce a spatial modulation of the magnetization in the form of stripes or bubbles. Our findings are consistent with recent observations in the bilayer ruthenate Sr$_3$Ru$_2$O$_7$.
Theoretical studies of the metamagnetism and anomalous phase of Sr3Ru2O7 have focused on the role of van Hove singularities, although much experimental evidence points towards quantum criticality having a large effect. We investigate the magnetic and thermodynamic properties of systems where magnetic field tunes through such a peak in the electronic density of states. We study the generic case of a van Hove singularity in 2D. We see that in combination with the requirement of number conservation and interaction effects the peak in the density of states produces several interesting phenomena in…
We show that the metamagnetic transition in Sr$_4$Ru$_3$O$_{10}$ bifurcates into two transitions as the field is rotated away from the conducting planes. This two-step process comprises partial or total alignment of moments in ferromagnetic bands followed by an itinerant metamagnetic transition whose critical field increases with rotation. Evidence for itinerant metamagnetism is provided by the Shubnikov-de Hass effect which shows a non-trivial evolution of the geometry of the Fermi surface and an enhancement of the quasiparticles effective-mass across the transition. The metamagnetic response…
The nature of the emergent phase near a putative quantum critical point in the bilayer ruthenate Sr$_3$Ru$_2$O$_7$ has been a recent subject of intensive research. It has been suggested that this phase may possess electronic nematic order(ENO). In this work, we investigate the possibility of nematic domain formation in the emergent phase, using a phenomenological model of electrons with ENO and its coupling to lattice degrees of freedom. The resistivity due to the scattering off the domain walls is shown to closely follow the ENO parameter. Our results provide qualitative explanations for the …
Tuning of electronic density-of-states singularities is a common route to unconventional metal physics. Conceptually, van Hove singularities are realized only in clean two-dimensional systems. Little attention has therefore been given to the disordered (dirty) limit. Here, we provide a magnetotransport study of the dirty metamagnetic system calcium-doped strontium ruthenate. Fermi liquid properties persist across the metamagnetic transition, but with an unusually strong variation of the Kadowaki-Woods ratio. This is revealed by a strong decoupling of inelastic electron scattering and electroni…
We report a detailed investigation into the metamagnetism of Sr3Ru2O7 at low temperatures for the magnetic field parallel to the ruthenium oxygen planes. The metamagnetism is studied as a function of temperature, magnetic field and sample quality using magnetisation, magnetotransport and specific heat as probes. From hysteretic behaviour in the magnetisation, we confirm earlier work and observe a finite temperature critical point at (5 T, >0.25 K). In our highest quality samples two-step metamagnetic transitions are additionally observed at 5.8 T and at 6.3 T, which coincide with a range of br…
The quasistatic approach is used to analyze the criterion of ferromagnetism for two-dimensional (2D) systems with the Fermi level near Van Hove (VH) singularities of the electron spectrum. It is shown that the spectrum of spin excitations (paramagnons) is positively defined when the interaction between electrons and paramagnons, determined by the Hubbard on-site repulsion U, is sufficiently large. Due to incommensurate spin fluctuations near the ferromagnetic quantum phase transition, the critical interaction Uc remains finite at VH filling and exceeds considerably its value obtained from the …
We use the quasistatic approach to analyze the criterion of ferromagnetism for two-dimensional (2D) systems with the Fermi level near Van Hove singularities (VHS) of the electronic spectrum. It is shown that the spectrum of spin excitations (paramagnons) is positively defined when the interaction I between electrons and paramagnons, which corresponds to the Hubbard on-site repulsion U, is sufficiently large. The critical interactions I_c and U_c remain finite at Van Hove filling and exceed considerably their values obtained from the Stoner criterion due to incommensurate spin fluctuations whic…
The most salient features observed around a metamagnetic transition in Sr3Ru2O7 are well captured in a simple model for spontaneous Fermi surface symmetry breaking under a magnetic field, without invoking a putative quantum critical point. The Fermi surface symmetry breaking happens in both a majority and a minority spin band but with a different magnitude of the order parameter, when either band is tuned close to van Hove filling by the magnetic field. The transition is second order for high temperature T and changes into first order for low T. The first order transition is accompanied by a m…
This article describes the Fermi surface properties of CeRu$_2$Si$_2$ and its alloy systems CeRu$_2$(Si$_x$Ge$_{1-x}$)$_2$ and Ce$_x$La$_{1-x}$Ru$_2$Si$_2$ studied by the de Haas - van Alphen (dHvA) effect. We pay particular attention to how the Fermi surface properties and the f electron state change with magnetic properties, in particular how they change associated with metamagnetic transition and quantum phase transition. After summarizing the important physical properties of CeRu$_2$Si$_2$, we present the magnetic phase diagrams of CeRu$_2$(Si$_x$Ge$_{1-x}$)$_2$ and Ce$_x$La$_{1-x}$Ru$_2$S…
The interplay of magnetic and superconducting fluctuations in two dimensional systems with van Hove singularities in the electronic spectrum is considered within the functional renormalization group (fRG) approach. While the fRG flow has to be stoped at a certain minimal temperature T_RG^min, we study temperature dependence of magnetic and superconducting susceptibilities both, above and below T_RG^min, which allows to obtain the resulting ground state phase diagram. Close to half filling the fRG approach yields two quantum phase transitions: from commensurate antiferromagnetic to incommensura…
We investigate a competition of tendencies towards ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization group technique using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved, lies in the vicinity of van Hove singularity points and perform an account of the self-energy corrections. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relatively to van Hove singularity (VHS). For the Fermi level above VHS we find at low temper…
The electronic structure of the perovskite La$_{1-x}$Sr$_x$CoO$_3$ has been obtained as a function of Sr substitution and volume from a series of generalized-gradient-corrected, full-potential, spin-density-functional band structure calculations. The energetics of different spin configurations are estimated using the fixed-spin-moment (FSM) method. From the total energy vs spin magnetic moment curve for LaCoO$_3$ the ground state is found to be nonmagnetic with the Co ions in a low-spin (LS) state, a result that is consistent with the experimental observations. Somewhat higher in energy, we fi…
We investigate the possibility of ferromagnetic ordering in the non-degenerate Hubbard model on the face-centered cubic lattice within the functional renormalization group technique using temperature as a scale parameter. We assume the relations between nearest, next-nearest, and next-next-nearest hopping parameters providing higher order (giant) van Hove singularity of the density of states. The ferromagnetic instability formation with lowering temperature is described consistently in the one-loop approximation for a one-particle irreducible vertex of two-particle electron interaction. The ch…
The local spectroscopic signatures of metamagnetic criticality in Sr3Ru2O7 were explored using scanning tunneling microscopy (STM). Singular features in the tunneling spectrum were found close to the Fermi level, as would be expected in a Stoner picture of itinerant electron metamagnetism. These features showed a pronounced magnetic field dependence across the metamagnetic critical point, which cannot be understood in terms of a naive Stoner theory. In addition, a pseudo-gap structure was observed over several tens of meV, accompanied by a c(2x2) superstructure in STM images. This result repre…
We report an electrical transport study in Ca$_{2-x}$Sr$_{x}$RuO$_4$ single crystals at high magnetic fields ($B$). For $x =0.2$, the Hall constant $R_{xy}$ decreases sharply at an anisotropic metamagnetic (MM) transition reaching its value for Sr$_2$RuO$_4$ at high fields. A sharp decrease in the $A$ coefficient of the resistivity $T^2$-term and a change in the structure of the angular magnetoresistance oscillations (AMRO) for $B$ rotating in the planes, confirms the reconstruction of the Fermi surface (FS). Our observations and LDA calculations indicate a strong dependence of the FS on the C…
We study symmetry-broken phases in twisted bilayer graphene at small filling above charge neutrality and at Van Hove filling. We argue that the Landau functionals for the particle-hole order parameters at these fillings both have an approximate SU(4) symmetry, but differ in the sign of quartic terms. We determine the order parameter manifold of the ground state and analyze its excitations. For small fillings, we find a strong 1st-order transition to an SU(3)$\otimes$U(1) manifold of orders that break spin-valley symmetry and induce a 3-1 splitting of fermionic excitations. For Van Hove filling…
A renormalization group treatment of the Kondo model with logarithmic Van Hove singularity in the electron density of states is performed within next-leading order scaling, different magnetic phases being considered. The effective coupling constant remains small, renormalized magnetic moment and spin-fluctuation frequency decreasing by several orders of magnitude. Thus wide non-Fermi-liquid behavior regions are found from the scaling trajectories in a broad interval of the bare coupling parameter. Applications to itinerant magnetism theory are discussed.
A scaling consideration of the Kondo lattices is performed with account of logarithmic Van Hove singularities (VHS) in the electron density of states. The scaling trajectories are presented for different magnetic phases. It is demonstrated that VHS lead to a considerable increase of the non-Fermi-liquid behavior region owing to softening of magnon branches during the renormalization process. Although the effective coupling constant remains moderate, renormalized magnetic moment and spin-fluctuation frequency can decrease by several orders of magnitude. A possible application to f-systems and w…
A thermodynamic and transport study of Sr4Ru3O10 as a function of temperature and magnetic field is presented. The central results include a growing specific heat C with increasing field B, a magnetic contribution to C/T at low temperatures proportional to -log(T), an abrupt jump and a peak in C/T at 2.90 T and 7 T for B||ab-plane and B||c-axis, respectively, and corresponding changes in the low T power laws of the resistivity. The novelty of this work lies in the fact that this system is strongly anisotropic displaying spontaneous ferromagnetism along the c-axis and an intralayer metamagnetic…
We report high field de Haas-van Alphen (dHvA) effect measurements in CeRh$_2$Si$_2$ both below and above the first-order 26 T metamagnetic transition from an antiferromagnetic to a polarized paramagnetic state. The dHvA frequencies observed above the transition are much higher than those observed below, implying a drastic change of the Fermi-surface size. The dHvA frequencies above the transition and their angular dependence are in good agreement with band-structure calculations for LaRh$_2$Si$_2$, which correspond to CeRh$_2$Si$_2$ with localized $f$ electrons. Given that the $f$ electrons a…
We study the electronic instabilities of doped bilayer silicene using the random phase approximation. In contrast to the singlet $d+id'$ superconductivity at the low doping region, we find that the system is an itinerant ferromagnet in the narrow doping regions around the Van Hove singularities, and a triplet $p+ip'$ superconductor in the vicinity of these regions. Adding a weak Kane-Mele spin-orbit coupling to the system further singles out the time-reversal invariant equal-spin helical $p+ip'$ pairing as the leading instability. The triplet pairing identified here is driven by the ferromagne…
Motivated by measurements of compressibility and STM spectra in twisted bilayer graphene, we analyze the pattern of symmetry breaking for itinerant fermions near a van Hove singularity. Making use of an approximate SU(4) symmetry of the Landau functional, we show that the structure of the spin/isospin order parameter changes with increasing filling via a cascade of transitions. We compute the feedback from different spin/isospin orders on fermions and argue that each order splits the initially 4-fold degenerate van Hove peak in a particular fashion, consistent with the STM data and compressibi…
The Fermi surface topology plays an important role in the macroscopic properties of metals. It can be particularly sensitive to electron correlation, which appears to be especially significant for the weak itinerant ferromagnet ZrZn$_{2}$. Here, we look at the differences in the predicted Fermi surface sheets of this metallic compound in its paramagnetic phase for both density functional theory (DFT) and the combination of DFT with dynamical mean field theory (DFT+DMFT). The theoretical spectral functions evaluated at the Fermi level were used along with calculations of the electron-positron m…
The bilayer ruthenate Sr_3Ru_2O_7 has been cited as a textbook example of itinerant metamagnetic quantum criticality. However, recent studies of the ultra-pure system have revealed striking anomalies in magnetism and transport in the vicinity of the quantum critical point. Drawing on new experimental data, we propose that the anomalous phase behavior can be accommodated by a mechanism which relies on the effects of strong magnetoelastic coupling. We argue that the phenomenological theory identified here is more generic and raises the possibility of quantum tricritical behaviour.
The microscopic basis for the stability of itinerant ferromagnetism in correlated electron systems is examined. To this end several routes to ferromagnetism are explored, using both rigorous methods valid in arbitrary spatial dimensions, as well as Quantum Monte Carlo investigations in the limit of infinite dimensions (dynamical mean-field theory). In particular we discuss the qualitative and quantitative importance of (i) the direct Heisenberg exchange coupling, (ii) band degeneracy plus Hund's rule coupling, and (iii) a high spectral density near the band edges caused by an appropriate latti…
We report experimental evidence of emergent broken symmetry Fermi liquid state in an isolated single crystalline nanorod of $\rm Pr_2 Ir_2 O_7$. We find clear signature of the onset of the Fermi liquid behavior at low temperature marked by the sign inversion of magnetoresistance from negative at high temperature, characteristic of incoherent Kondo scattering, to positive as well as a $\rm T^2$ dependence of resistivity at low temperature. A resistive anomaly is observed, which is accompanied by thermal hysteresis in the presence of magnetic field, suggesting itinerant metamagnetism. The observ…
The magnetic ground state of (Sr$_{1-x}$Ca$_x$)$_3$Ru$_2$O$_7$ (0 $\leq x \leq$ 1) is complex, ranging from an itinerant metamagnetic state (0 $\leq x <$ 0.08), to an unusual heavy-mass, nearly ferromagnetic (FM) state (0.08 $< x <$ 0.4), and finally to an antiferromagnetic (AFM) state (0.4 $\leq x \leq$ 1). In this report we elucidate the electronic properties for these magnetic states, and show that the electronic and magnetic properties are strongly coupled in this system. The electronic ground state evolves from an AFM quasi-two-dimensional metal for $x =$ 1.0, to an Anderson localized sta…
We derive, by means of an extended Gutzwiller wavefunction and within the Gutzwiller approximation, the phase diagram of the Kondo lattice model. We find that generically, namely in the absence of nesting, the model displays an $f$-electron Mott localization accompanied by a discontinuous change of the conduction electron Fermi surface as well as by magnetism. When the non interacting Fermi surface is close to nesting, the Mott localization disentangles from the onset of magnetism. First the paramagnetic heavy fermion metal turns continuously into an itinerant magnet - the Fermi surface evolve…
The topology of isoenergetic surfaces in reciprocal space for simple (sc), body-centered (bcc), and face-centered (fcc) cubic lattices is investigated in detail in the tight-binding approximation, taking into account the transfer integrals between the nearest and next neighbors $t$ and $t'$. It is shown that, for values $τ= t'/t = τ_\ast$ corresponding to a change in the topology of surfaces, lines and surfaces of $\mathbf k$-van Hove points can be formed. With a small deviation of $τ$ from these singular values, the spectrum in the vicinity of the van Hove line (surface) is replaced by a weak…
We present results of a detailed theoretical study of the electronic, magnetic, and structural properties of the chalcogenide parent system FeSe using a fully charge self-consistent implementation of the density functional theory plus dynamical mean-field theory (DFT+DMFT) method. In particular, we predict a remarkable change of the electronic structure of FeSe which is accompanied by a complete reconstruction of the Fermi surface topology (Lifshitz transition) upon a moderate expansion of the lattice volume. The phase transition results in a change of the in-plane magnetic nesting wave vector…
Using density functional plus dynamical mean-field theory method (DFT+DMFT) with full self-consistency over the charge density, we study the effect of electronic correlations on the electronic structure, magnetic properties, orbital-dependent band renormalizations, and Fermi surface of the tetragonal phase of bulk FeS. We perform a direct structural optimization of the $P_4/nmm$ crystal structure of paramagnetic FeS, with respect to the lattice constant $a$ and the internal coordinate $z_\mathrm{S}$ of atom S. Our results show an anomalous sensitivity of the electronic structure and magnetic p…
The interplay of spin-orbit-coupling and strong electronic correlations is studied for the single-layer and the bilayer compound of the strontium ruthenate Ruddlesden-Popper series by a combination of first-principles band-structure theory with mean-field rotationally invariant slave bosons. At equilibrium strongly renormalized (spin-orbit-split) quasiparticle bands are traced and a thorough description of the low-energy regime for the nearly ferromagnetic bilayer system in accordance with experimental data is presented. The metamagnetic response of Sr$_3$Ru$_2$O$_7$ in finite magnetic field $…
Magneto-optical signatures of plateau states in the kagome spin-ice HoAgGe
Augsburg University（奥格斯堡大学）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；Colorado State University（科罗拉多州立大学）；Beihang University（北京航空航天大学）；Laboratoire National des Champs Magnétiques Intenses, LNCMI-EMFL, CNRS UPR3228, Univ. Grenoble Alpes, Univ. Toulouse, Univ. Toulouse 3, INSA-T（强磁场国家实验室，LNCMI-EMFL，法国国家科学研究中心UPR3228，格勒诺布尔阿尔卑斯大学，图卢兹大学，图卢兹第三大学，国立应用科学学院-图卢兹）；Charles University（查理大学）；National Institute of Chemical Physics（国立化学物理研究所）
Comprehensive magnetic-field-orientation dependent studies of the susceptibility and de Haas-van Alphen effect have been carried out on single crystals of the filled skutterudites PrOs$_4$As$_{12}$ and LaOs$_4$As$_{12}$ using magnetic fields of up to 40~T. Several peaks are observed in the low-field susceptibility of PrOs$_4$As$_{12}$, corresponding to cascades of metamagnetic transitions separating the low-field antiferromagnetic and high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments show that the Fermi-surface topologies of PrOs$_4$As$_{12}$ in its PMM phase and L…
