Field-induced Charge Density Wave Research Articles

Steady off-diagonal long-range order state in a half-filled dimerized Hubbard chain induced by a resonant pulsed field

We show that a resonant pulsed field can induce a steady superconducting state even in the deep Mott insulating phase of the dimerized Hubbard model. The superconductivity found here in the non-equilibrium steady state is due to the $\eta $-pairing mechanism, characterized by the existence of the off-diagonal long-range order (ODLRO), and is absent in the ground-state phase diagram. The key of the scheme lies in the generation of the field-induced charge density wave (CDW) state that is from the valence bond solid. The dynamics of this state resides in the highly-excited subspace of dimerized Hubbard model and is dominated by a $\eta $-spin ferromagnetic model. The decay of such long-living excitation is suppressed because of energy conservation. We also develop a dynamical method to detect the ODLRO of the non-equilibrium steady state. Our finding demonstrates that the non-equilibrium many-body dynamics induced by the interplay between the resonant external field and electron-electron interaction is an alternative pathway to access a new exotic quantum state, and also provides an alternative mechanism for enhancing superconductivity.

Interplay between charge density wave order and magnetic field in the nonmagnetic rare-earth tritelluride LaTe3

Charge density wave (CDW) states in solids bear an intimate connection to underlying fermiology. Modification of the latter by a suitable perturbation provides an attractive handle to unearth novel CDW states. Here, we combine extensive magnetotransport experiments and first-principles electronic structure calculations on a non-magnetic tritelluride LaTe$_{3}$ single crystal to uncover phenomena rare in CDW systems: $(i)$ hump-like feature in the temperature dependence of resistivity at low temperature under application of magnetic field, which moves to higher temperature with increasing field strength, $(ii)$ highly anisotropic large transverse magnetoresistance (MR) upon rotation of magnetic field about current parallel to crystallographic c-axis, (iii) anomalously large positive MR with spike-like peaks at characteristic angles when the angle between current and field is varied in the bc-plane, (iv) extreme sensitivity of the angular variation of MR on field and temperature. Moreover, our Hall measurement reveals remarkably high carrier mobility $\sim$ 33000 cm$^{2}$/Vs, which is comparable to that observed in some topological semimetals. These novel observations find a comprehensive explication in our density functional theory (DFT) and dynamical mean field theory (DMFT) calculations that capture field-induced electronic structure modification in LaTe$_{3}$. The band structure theory together with transport calculations suggest the possibility of a second field-induced CDW transition from the field-reconstructed Fermi surface, which qualitatively explains the hump in temperature dependence of resistivity at low temperature. Thus, our study exposes the novel manifestations of the interplay between CDW order and field-induced electronic structure modifications in LaTe$_{3}$, and establishes a new route to tune CDW states by perturbations like magnetic field.

Quantum criticality of magnetic catalysis in two-dimensional correlated Dirac fermions

We study quantum criticality of the magnetic field induced charge density wave (CDW) order in correlated spinless Dirac fermions on the $\pi$-flux square lattice at zero temperature as a prototypical example of the magnetic catalysis, by using the infinite density matrix renormalization group. It is found that the CDW order parameter $M(B)$ exhibits an anomalous magnetic field $(B)$ scaling behavior characteristic of the $(2+1)$-dimensional chiral Ising universality class near the quantum critical point, which leads to a strong enhancement of $M(B)$ compared with a mean field result. We also establish a global phase diagram in the interaction-magnetic field plane for the fermionic quantum criticality.

Charge density waves beyond the Pauli paramagnetic limit in 2D systems

Two-dimensional materials are ideal candidates to host Charge Density Waves (CDWs) that exhibit paramagnetic limiting behavior, similar to the well-known case of superconductors. Here, we study how CDWs in two-dimensional systems can survive beyond the Pauli limit when they are subjected to a strong magnetic field by developing a generalized mean-field theory of CDWs under Zeeman fields that includes incommensurability, imperfect nesting, and temperature effects and the possibility of a competing or coexisting Spin Density Wave (SDW) order. Our numerical calculations yield rich phase diagrams with distinct high-field phases above the Pauli limiting field. For perfectly nested commensurate CDWs, a q-modulated CDW phase that is completely analogous to the superconducting Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase appears at high fields. In the more common case of imperfect nesting, the commensurate CDW ground state undergoes a series of magnetic-field-induced phase transitions first into a phase where commensurate CDW and SDW coexist and subsequently into another phase where CDW and SDW acquire a q-modulation that is, however, distinct from the pure FFLO CDW phase. The commensurate CDW + SDW phase occurs for fields comparable to but less than the Pauli limit and survives above it. Thus, this phase provides a plausible mechanism for the CDW to survive at high fields without the need for forming the more fragile FFLO phase. We suggest that the recently discovered 2D materials like the transition metal dichalcogenides offer a promising platform for observing such exotic field-induced CDW phenomena.

Quantum oscillations and magnetoresistance in type-II Weyl semimetals: Effect of a field-induced charge density wave

Recent experiments on type-II Weyl semimetals such as WTe$_2$, MoTe$_2$, Mo$_x$W$_{1-x}$Te$_2$ and WP$_2$ reveal remarkable transport properties in presence of a strong magnetic field, including an extremely large magnetoresistance and an unusual temperature dependence. Here, we investigate magnetotransport via the Kubo formula in a minimal model of a type-II Weyl semimetal taking into account the effect of a charge density wave (CDW) transition, which can arise even at weak coupling in the presence of a strong magnetic field because of the special Landau level dispersion of type-II Weyl systems. Consistent with experimental measurements we find an extremely large magnetoresistance with close to $B^2$ scaling at particle-hole compensation, while in the extreme quantum limit there is a transition to a qualitatively new scaling with approximately $B^{0.75}$. We also investigate the Shubnikov-de Haas effect and find that the amplitude of the resistivity quantum oscillations are greatly enhanced below the CDW transition temperature which is accompanied by an unusual non-monotonous (non-Lifshitz-Kosevich) temperature dependence.

Nuclear magnetic resonance in high magnetic field: Application to condensed matter physics

In this review, we describe the potentialities offered by the nuclear magnetic resonance (NMR) technique to explore at a microscopic level new quantum states of condensed matter induced by high magnetic fields. We focus on experiments realised in resistive (up to 34 T) or hybrid (up to 45 T) magnets, which open a large access to these quantum phase transitions. After an introduction on NMR observables, we consider several topics: quantum spin systems (spin–Peierls transition, spin ladders, spin nematic phases, magnetisation plateaus, and Bose–Einstein condensation of triplet excitations), the field-induced charge density wave (CDW) in high-Tc superconductors, and exotic superconductivity including the Fulde–Ferrel–Larkin–Ovchinnikov superconducting state and the field-induced superconductivity due to the Jaccarino–Peter mechanism. Dans cette revue, nous décrivons les opportunités offertes par la résonance magnétique nucléaire (RMN) pour étudier les propriétés microscopiques des nouveaux états quantiques de la matière induits par les champs magnétiques intenses. Nous mettons l'accent sur les expériences réalisées dans des bobines résistives (jusqu'à 34 T) ou hybrides (jusqu'à 45 T), qui ouvrent un large accès à ce type de transitions quantiques. Après avoir introduit les quantités observables par RMN, nous considérons plusieurs domaines de recherche : les systèmes de spins quantiques (la transition de spin–Peierls, les échelles de spin, les phases nématiques de spin, les plateaux d'aimantation et la condensation de Bose–Einstein des excitations triplets), l'onde de densité de charge induite sous champ dans les supraconducteurs à haute Tc, et la supraconductivité exotique, avec la phase supraconductrice Fulde–Ferrel–Larkin–Ovchinnikov et la supraconductivité induite sous champ de type Jaccarino–Peter.

Field-Induced CDW Phases in a Quasi-One-Dimensional Organic Conductor, HMTSF-TCNQ Under Pressure of 1 GPa in Magnetic Field of 31 T

HMTSF-TCNQ is a quasi-one-dimensional organic conductor which undergoes CDW(charge density wave) transition at 30 K at ambient pressure, where HMTSF-TCNQ is hexamethylenetetraselena fulvalene-tetracyano quino dimethane. This CDW is suppressed by the pressure of 1 GPa. At this pressure, we found field-induced successive hysteretic transitions in magnetoresistance. This reminds us of the successive field-induced SDW (spin density wave) phases in TMTSF2X salts. However, the field range of interest is 2–3 times higher than that of TMTSF2X salts. Therefore, we need really high field to examine these properties. It is very likely that the field induced phases are of field induced CDW (FICDW), where quantum Hall effect and many interesting phenomena are expected like in the case of FISDW. Together with the magnetoresistance study up to the field of 31 Tesla and at temperatures down to 0.4 K in various magnetic field angles respective to the crystal axes, we examined the angular dependence of magnetoresistance oscillations(AMRO). It turned out that AMRO demonstrates clearly the occurrence of field-induced phase rather than the magneto-resistance by field sweep. Since the Hall resistance, R xy in the field-induced phases showed stepwise plateau structure against the field sweep, and its strength was in the order of magnitude of h/e 2 per molecular sheet, the Hall effect is very suggestive of quantum Hall effect.

Electronic crystals: an experimental overview

This article reviews the static and dynamic properties of spontaneous superstructures formed by electrons. Representations of such electronic crystals are charge density waves (CDW) and spin density waves in inorganic as well as organic low-dimensional materials. A special attention is paid to the collective effects in pinning and sliding of these superstructures, and the glassy properties at low temperature. Charge order and charge disproportionation which occur in organic materials resulting from correlation effects are analysed. Experiments under magnetic field, and more specifically field-induced CDWs are discussed. Properties of meso- and nanostructures of CDWs are also reviewed.

Field-induced CDW in HMTSF-TCNQ

Field-induced successive transitions were observed in magnetoresistance in the quasi-one-dimensional organic conductor, HMTSF-TCNQ, hexamethylene-tetraselena-fulvalene-tetracyanoquinodimethane. The magnetoresistance exhibits kink transitions accompanying hysteresis at pressures around 1GPa, but neither at p=0 nor at 2GPa. At p=0 and below 30K, this material undergoes charge density wave (CDW) state, which is suppressed around 1GPa, where successive transitions are observed. Since these behavior is only observed at the boundary in pressure between insulator and metal, and the nature of the insulating state is CDW at p=0, it is strongly suggested that the successive transitions observed in magnetoresistance might be associated with CDW, accordingly a field-induced CDW by the one-dimensionalization by strong magnetic field ranging from 10 to 30T. The behaviors are compared with previously claimed FICDW and the established FISDW (field-induced-spin-density-wave).

High magnetic field induced charge density waves and sign reversal of the Hall coefficient ingraphite

We report on the investigation of magnetic field induced charge density waves and Hallcoefficient sign reversal in a quasi-two-dimensional electronic system of highly orientedpyrolytic graphite under very strong magnetic field. The change of Hall sign coefficientfrom negative to positive occurs at low temperature and high magnetic field just after thecharge density wave transition, suggesting the role of hole-like quasi-particles inthis effect. Angular dependent measurements show that the charge density wavetransition and Hall sign reversal fields follow the magnetic field component along thec-axis of graphite.

Magnetic field-induced charge-density-wave transitions: The role of the orbital and Pauli effects

Abstract Due to a low transition temperature and, correspondingly, a small energy gap, the charge-density-wave (CDW) state of the layered organic metal α - ( BEDT - TTF ) 2 KHg ( SCN ) 4 is very sensitive to pressure and magnetic field. The latter couples to the CDW via two competing mechanisms: Pauli paramagnetism and orbital motion of charge carriers in a magnetic field. We study the interplay between the Pauli and orbital effects under a pressure of 2.8 kbar, in the region of the field-induced CDW (FICDW) instability. We find that, in agreement with theoretical predictions, the FICDW state is enhanced when the Zeeman splitting becomes commensurate with the orbital quantization.

Hierarchy of the density-wave states and superconductivity in the organic conductor α-(BEDT-TTF)2KHg(SCN)4

Abstract The layered organic conductor α-(BEDT-TTF)2KHg(SCN)4 exhibits a phase transition into the charge-density-wave (CDW) state at an unusually low temperature. This leads to a very high sensitivity of the ground state to magnetic field and pressure. We present a number of novel field-induced CDW states originating from the superposition of the strong paramagnetic and quantized orbital effects of the magnetic field. At temperatures below 0.3 K the CDW phase coexists with a superconducting phase. Surprisingly, the CDW formation is found to remarkably increase the superconducting onset temperature.

The investigation of transport properties of mesoscopic graphite in high magnetic field

Abstract The electrical transport properties of mesoscopic graphite have been investigated in a gate voltage configuration. Few layer graphene structures made from Kish graphite exhibit Shubnikov-de Haas (SdH) oscillations in magnetic fields up to 33 T, with a strong gate voltage dependence. A two band model can be used to explain the linear dependence of the SdH frequency on the gate voltage. The temperature dependence of the SdH oscillation amplitude allows the determination of the effective masses of the carriers, which remain comparable between mesoscopic and bulk graphite samples. However, mesoscopic graphite thinner than 130 nm does not exhibit the field induced charge density wave transition seen in bulk samples above 25 T at low temperatures.

Landau Quantization Effects in the Charge-Density-Wave System(Per)2M(mnt)2(whereM=Auand Pt)

A finite transfer integral t(a) orthogonal to the conducting chains of a highly one-dimensional metal gives rise to empty and filled bands that simulate an indirect-gap semiconductor upon formation of a charge-density wave (CDW). In contrast to semiconductors such as Ge and Si with band gaps approximately 1 eV, the CDW system possesses an indirect gap with a greatly reduced energy scale, enabling moderate laboratory magnetic fields to have a major effect. The consequent variation of the thermodynamic gap with magnetic field due to Zeeman splitting and Landau quantization enables the electronic band structure parameters (transfer integrals, Fermi velocity) to be determined accurately. These parameters reveal the orbital quantization limit to be reached at approximately 20 T in (Per)2M(mnt)(2) salts, making them highly unlikely candidates for a recently proposed cascade of field-induced CDW states.

High magnetic field induced charge density wave state in a quasi-one-dimensional organic conductor.

The quasi-one-dimensional organic conductor (Per)2Pt(mnt)2 exhibits a charge density wave ground state below 8 K. Magnetoresistance and magnetization measurements show that the charge density wave is suppressed with magnetic fields of order 20 T, above which a high resistance state, with a cascade of subphases, appears. This new state, tentatively identified as a field induced charge density wave, reenters a low resistance state above 40 T. The results are presented in light of theoretical work [D. Zanchi et al. Phys. Rev. B 53, 1240 (1996)]] involving field induced charge density wave ground states in high magnetic fields.

New electronic phase transitions in α -(BEDT-TTF)2KHg(SCN)4

\alpha-(BEDT-TTF)2KHg(SCN)4 is considered to be in the charge-density-wave (CDW) state below 8 K. We present new magnetoresistance data suggesting that the material undergoes a series of field-induced CDW (FICDW) transitions at pressures slightly exceeding the critical pressure Pc at which the zero-field CDW state is destroyed. Further, we argue that a novel kind of FICDW transitions, entirely determined by a superposition of the strong Pauli and quantizing orbital effects of magnetic field on the CDW wavevector, arises when the field is strongly tilted towards the conducting layers. These new transitions can take place even in the case of a relatively well nested Fermi surface. Finally we report on the superconducting (SC) state and its coexistence with the CDW in the title compound under quasi-hydrostatic pressure. Below Pc the material is most likely a heterogeneous SC/CDW mixture, with the SC phase persisting down to ambient pressure. The SC onset temperature appears to drastically increase upon entering the SC/CDW coexistence region.

Interplay between the orbital quantization and Pauli effect in a charge-density-wave organic conductor

The interlayer magnetoresistance of the low-dimensional organic metal α-(BEDT–TTF) 2KHg(SCN) 4 under pressure shows features which are likely associated with theoretically predicted field-induced charge-density-wave (FICDW) transitions. At ambient pressure, a magnetic field strongly tilted towards the conducting layers induces a series of hysteretic anomalies. We attribute these anomalies to a novel kind of FICDW originating from a superposition of the orbital quantization of the nesting vector and Pauli effect on the charge-density wave.

Theory of magnetic field-induced charge-density-wave phases

We elaborate an analytical theory of a cascade of magnetic field-induced charge-density-wave (FICDW) phases. It is shown that the following features distinguish it from the well-known spin-density-wave cascade: (1) the FICDW phases exist at temperatures much lower than the characteristic CDW transition temperature at H=0; (2) the cascade of the FICDW phases dramatically changes at certain directions of a magnetic field due to an interplay of Zeeman spin-splitting and electron motion along open Fermi surfaces. Theoretical results are compared with the recent experimental attempts to reveal FICDW phases in the organic conductors α-(ET)2MHg(SCN)4(M=K, Tl, Rb, etc.).

Pauli and orbital effects of magnetic field on charge density waves

Taking into account both Pauli and orbital effects of external magnetic field we compute the mean field phase diagram for charge density waves in quasi-one-dimensional electronic systems. The magnetic field can cause transitions to CDW states with two types of the shifts of wave vector from its zero-field value. It can also stabilize the field-induced charge density wave. Furthermore, the critical temperature shows peaks at a new kind of magic angles.

Phase diagram for charge-density waves in a magnetic field

The influence of an external magnetic field on a quasi one-dimensional system with a charge density wave (CDW) instability is treated within the random phase approximation which includes both CDW and spin density wave correlations. We show that the CDW is sensitive to both orbital and Pauli effects of the field. In the case of perfect nesting, the critical temperature decreases monotonously with the field, and the wave vector of the instability starts to shift above some critical value of magnetic field. Depending on the ratio between the spin and charge coupling constants and on the direction of the applied magnetic field, the wave vector shift is either parallel ($CDW_x$ order) or perpendicular ($CDW_y$ order) to the most conducting direction. The $CDW_x$ order is a field dependent linear combination of the charge and spin density waves and is sensible only to the Pauli effect. The wave vector shift in $CDW_y$ depends on the interchain coupling, but the critical temperature does not. This order is affected by the confinement of the electronic orbits. By increasing the relative strength of the orbital effect with respect to the Pauli effect, one can destroy the $CDW_y$, establishing either a $CDW_x$, or a $CDW_0$ (corresponding to perfect nesting wave vector). We also show that by increasing the imperfect nesting parameter, one passes from the regime where the critical temperature decreases with the field to the regime where it is initially enhanced by the orbital effect and eventually suppressed by the Pauli effect. For a bad nesting, the quantized phases of the field-induced CDW appear.