Field-induced Quantum Criticality Research Articles

Field-Induced Quantum Criticality in Two-Coupled Two-Leg Heisenberg Ladders

We use the bond mean field theory, which is based on the Jordan–Wigner fermionization, to investigate the quantum critical behavior of a system composed of two-coupled Heisenberg Spin-[Formula: see text] two-leg ladders in the presence of an applied magnetic field. By examining the dependence of the ground state on the magnetic field for different coupling constants, we investigate the field-induced quantum criticality. The magnetization exhibits distinct plateaus: a zero magnetization plateau for fields below a threshold value of the field [Formula: see text] and a saturation plateau for fields exceeding a second critical value [Formula: see text]. The spin bond parameters are calculated and found to show a critical behavior at [Formula: see text].

Entropic topography associated with field-induced quantum criticality in a magnetic insulator DyVO4

Exploration of low temperature phase transitions associated with quantum critical point is one of the most mystifying fields of research which is under intensive focus in recent times. In this work, through comprehensive experimental evidences, we report the possibility of achieving quantum criticality in the neighborhood of a magnetic field-tuned tricritical point separating paramagnetic, antiferromagnetic and metamagnetic phases in a magnetic insulator, DyVO4. Magnetic susceptibility and heat capacity indicate to the presence of a long-range second order antiferromagnetic transition at TN ~ 3.2 K. Field variation of Magnetic susceptibility and heat capacity, along with differential magnetic susceptibility and DC field dependent AC susceptibility gives evidence of the modification of the antiferromagnetic structure below the tricritical point; implying the presence of a field-induced first order metamagnetic transition which persists down to 1.8 K. Further, the magnetic field dependence of the thermodynamic quantity − dM/dT, which is related to magnetic Gruneisen parameter, approaches a minimum, followed by a crossover near 5 kOe to a maximum; along with a hyperbolic divergence in temperature response of dM/dT in the critical field regime. Temperature response of heat capacity at 5 kOe also shows a deviation from the conventional behavior. Entropic topography phase diagram allows tracking of the variation of the entropy, which indicates towards the emergence of the peak at quantum critical point into a V-shaped region at high temperatures. Our studies yield an inimitable phase diagram describing a tricritical point at which the second-order antiferromagnetic phase line terminates followed by a first order line of metamagnetic transition, as the temperature is lowered, leading to metamagnetic quantum critical end point.

Magnetic field induced quantum criticality and the Luttinger sum rule

We show that when there is a sudden transition from a small to a large Fermi surface at a field-induced quantum critical point, similar to what may have been observed in some heavy-fermion compounds, an additional term has to be taken into account in the Luttinger-Friedel sum rule.We calculate this additional term for a local model which has a field-induced quantum critical point (QCP) and show that it changes abruptly at the transition, such that it satisfies a generalized Luttinger-Friedel sum rule on each side of the transition, and characterizes the two Fermi-liquid phases separated by the QCP as a discrete (topological) index.

Magnetic field-induced Fermi surface reconstruction and quantum criticality in

We present detailed results of the field evolution of the de Haas–van Alphen (dHvA) effect in . A magnetic field-induced reconstruction of the Fermi surface is clearly shown to occur inside the antiferromagnetic state, in an applied field of around T, which is evidenced by the appearance of several new dHvA branches. The angular dependence of the dHvA frequencies reveals that the Fermi surfaces of at and are similar. The results suggest that the Ce-4f electrons in become itinerant at due to the Kondo effect, prior to the field-induced quantum critical point (QCP) at T. The electronic states at the field-induced QCP are therefore different from that of the pressure-induced QCP where a dramatic Fermi surface reconstruction occurs exactly at the critical pressure, indicating that multiple types of QCP may exist in .

Signature of frustrated moments in quantum critical CePd1−xNixAl

CePdAl with Ce $4f$ moments forming a distorted kagom\'e network is one of the scarce materials exhibiting Kondo physics and magnetic frustration simultaneously. As a result, antiferromagnetic (AF) order setting in at $T_{\mathrm{N}} = 2.7$~K encompasses only two thirds of the Ce moments. We report measurements of the specific heat, $C$, and the magnetic Gr\"uneisen parameter, $\Gamma_{\rm mag}$, on single crystals of CePd$_{1-x}$Ni$_x$Al with $x\leq 0.16$ at temperatures down to 0.05~K and magnetic fields $B$ up to $8$~T. Field-induced quantum criticality for various concentrations is observed with the critical field decreasing to zero at $x_c\approx 0.15$. Remarkably, two-dimensional (2D) AF quantum criticality of Hertz-Millis-Moriya type arises for $x=0.05$ and $x=0.1$ at the suppression of 3D magnetic order. Furthermore, $\Gamma_{\rm mag}(B)$ shows an additional contribution near $2.5$~T for all concentrations which is ascribed to correlations of the frustrated one third of Ce moments.

Multiple Metamagnetic Quantum Criticality in Sr_{3}Ru_{2}O_{7}.

Bilayer strontium ruthenate Sr_{3}Ru_{2}O_{7} displays pronounced non-Fermi liquid behavior at magnetic fields around 8T, applied perpendicular to the ruthenate planes, which previously has been associated with an itinerant metamagnetic quantum critical end point (QCEP). We focus on the magnetic Grüneisen parameter Γ_{H}, which is the most direct probe to characterize field-induced quantum criticality. We confirm quantum critical scaling due to a putative two-dimensional QCEP near 7.845(5)T, which is masked by two ordered phases A and B, identified previously by neutron scattering. In addition, we find evidence for a QCEP at 7.53(2)T and determine the quantum critical regimes of both instabilities and the effect of their superposition.

Converse effect of pressure on the quadrupolar and magnetic transition inCe3Pd20Si6

The heavy fermion compound Ce$_{3}$Pd$_{20}$Si$_{6}$ displays unconventional quantum criticality as the lower of two consecutive phase transitions is fully suppressed by magnetic field. Here we report on the effects of pressure as additional tuning parameter. Specific heat and electrical resistivity measurements reveal a converse effect of pressure on the two transitions, leading to the merging of both transitions at 6.2 kbar. The field-induced quantum criticality is robust under pressure tuning. We rationalize our findings within an extended version of the global phase diagram for antiferromagnetic heavy fermion quantum criticality.

Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2.

The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.

Field-induced quadrupolar quantum criticality inPrV2Al20

${\mathrm{PrV}}_{2}{\mathrm{Al}}_{20}$ is a heavy-fermion superconductor based on the cubic ${\mathrm{\ensuremath{\Gamma}}}_{3}$ doublet that exhibits nonmagnetic quadrupolar ordering below $\ensuremath{\sim}0.6$ K. Our magnetotransport study on ${\mathrm{PrV}}_{2}{\mathrm{Al}}_{20}$ reveals field-induced quadrupolar quantum criticality at ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}}\ensuremath{\sim}11$ T applied along the [111] direction. Near the critical field ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}}$ required to suppress the quadrupolar state, we find a marked enhancement of the resistivity $\ensuremath{\rho}(H,T)$, a divergent quasiparticle effective mass and concomitant non-Fermi-liquid (NFL) behavior [i.e., $\ensuremath{\rho}(T)\ensuremath{\propto}{T}^{n}$ with $n\ensuremath{\le}0.5$]. We also observe the Shubnikov--de Haas effect above ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}}$, indicating effective mass enhancement or ${m}^{*}/{m}_{0}\ensuremath{\sim}10$. This reveals the competition between the nonmagnetic Kondo effect and the intersite quadrupolar coupling which leads to pronounced NFL behavior in an extensive region of $T$ and ${\ensuremath{\mu}}_{0}H$ emerging from the quantum-critical point.

Magnetic field induced quantum criticality at a Lifshitz transition with interactions

Motivated by a discontinuous transition observed in CeIn3 in high magnetic fields, the effects of the Landau quantization and interactions on a Lifshitz transition are studied. The Landau quantization leads to a quasi-one-dimensional behavior for the direction parallel to the field. The repulsive Coulomb interactions give rise to a gas of strongly coupled particles. The density correlation function is calculated for a special long-ranged interaction potential. It is concluded that, in the ground state, an electron (or hole) pocket is emptied in a discontinuous fashion as a function of the chemical potential (or magnetic field). This discontinuity is gradually smeared by the temperature, in agreement with experiments for CeIn3.

Magnetic field-induced quantum criticality via new asymptotically AdS5 solutions

Using analytical methods, we derive and extend previously obtained numerical results on the low temperature properties of holographic duals to four-dimensional gauge theories at finite density in a nonzero magnetic field. We find a new asymptotically AdS5 solution representing the system at zero temperature. This solution has vanishing entropy density, and the charge density in the bulk is carried entirely by fluxes. The dimensionless magnetic field to charge density ratio for these solutions is bounded from below, with a quantum critical point appearing at the lower bound. Using matched asymptotic expansions, we extract the low temperature thermodynamics of the system. Above the critical magnetic field, the low temperature entropy density takes a simple form, linear in the temperature, and with a specific heat coefficient diverging at the critical point. At the critical magnetic field, we derive the scaling law s ∼ T1/3 inferred previously from the numerical analysis. We also compute the full scaling function describing the region near the critical point and identify the dynamical critical exponent: z = 3. These solutions are expected to holographically represent boundary theories in which strongly interacting fermions are filling up a Fermi sea. They are fully top–down constructions in which both the bulk and boundary theories have well-known embeddings in the string theory.Communicated by S F Ross

Quantum fluctuations and the magnetic ground state ofCe3Pd20Si6

The temperature and magnetic field dependence of neutron-scattering studies on the heavy fermion compound ${\text{Ce}}_{3}{\text{Pd}}_{20}{\text{Si}}_{6}$ are reported. Inelastic neutron scattering reveals two crystal-field excitations corresponding to the environments of the two distinct rare-earth locations within this cubic compound. Surprisingly, the ground states of the two individual Ce sites are inequivalent with the $4a$ site having a ${\ensuremath{\Gamma}}_{7}$ ground state, while the $8c$ site reveals a ${\ensuremath{\Gamma}}_{8}$ ground state. This is in contrast to the situation found in the analogous compound ${\text{Ce}}_{3}{\text{Pd}}_{20}{\text{Ge}}_{6}$, where the ${\ensuremath{\Gamma}}_{8}$ ground state is realized for both Ce sites. In addition, these results reveal an interaction between the $8c$ and $4a$ sites previously believed to be absent. The ground state was probed with uniaxial polarization analysis across the region in which field-induced quantum criticality has previously been determined. In zero applied magnetic field no long-range magnetic order could be determined. However, further evidence of field-induced quantum criticality is presented with the observation of diffuse scattering consistent with quantum fluctuations due to nearest-neighbor spin correlations between the two Ce sites.

Extremely Large and Anisotropic Upper Critical Field and the Ferromagnetic Instability in UCoGe

Magnetoresistivity measurements with fine tuning of the field direction on high quality single crystals of the ferromagnetic superconductor UCoGe show anomalous anisotropy of the upper critical field H c2 . H c2 for H ∥ b -axis ( H c2 b ) in the orthorhombic crystal structure is strongly enhanced with decreasing temperature with an S-shape and reaches nearly 20 T at 0 K. The temperature dependence of H c2 a shows upward curvature with a low temperature value exceeding 30 T, while H c2 c at 0 K is very small (∼0.6 T). Contrary to conventional ferromagnets, the decrease of the Curie temperature with increasing field for H ∥ b -axis marked by an enhancement of the effective mass of the conduction electrons appears to be the origin of the S-shaped H c2 b curve. These results indicate that the field-induced ferromagnetic instability or magnetic quantum criticality reinforces superconductivity.

Evidence for field-induced quantum critical route to a Fermi liquid in overdoped Tl2Ba2CuO6+x

We report an unanticipated transformation from a non-Fermi- to a Fermi-liquid state driven by magnetic field in a highly overdoped Tl2Ba2CuOe+x with Tc ∼ 15 K. From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid ρc = ρc(0) + AT2 features, accompanied by a field-linear magnetoresistance, appear above a temperature-dependent field HFL, which decreases linearly with decreasing temperature and points to a quantum critical point near the upper critical field HC2(0). The observed field-induced quantum criticality with a power-law diverging A(H) bears a striking resemblance to that of heavy-fermion superconductor CeCoIn5, suggesting a common underlying physics in these strongly correlated electron systems.

Field-induced quantum criticality of a spin-1/2 planar ferromagnet

The low-temperature critical properties and crossovers of a spin-½ planar ferromagnet in a longitudinal magnetic field are explored in terms of an anisotropic bosonic action, suitable to describe the spin model in the low-temperature regime. This is performed adopting a procedure which combines an averaging over dynamic degrees of freedom and the classical Wilson renormalization group transformation. Within this framework we get the phase boundary, ending in a quantum critical point, and general expressions for the correlation length and susceptibility as functions of the temperature and the applied magnetic field within the disordered phase. In particular, two crossovers occur decreasing the temperature with the magnetic field fixed at its quantum critical point value, which might be actually observable in complex magnetic compounds, as suggested by recent experiments.

Two-time Green’s function treatment of field-induced quantum criticality of a -dimensional easy-plane ferromagnet with longitudinal uniform interactions

Abstract The two-time Green’s function equation of motion method is employed to explore the low-temperature properties and crossovers close to the field-induced quantum critical point of a d -dimensional spin- 1/2 easy-plane ferromagnet with longitudinal uniform interactions. This is performed, on the ground of an exact mapping into an effective XY model in a transverse field, using the Tyablikov decoupling procedure, which is shown to provide, at zero temperature, the exact results recently obtained for the same model with arbitrary d and spin S . We determine the full structure of the phase diagram for different values of d and S = 1 / 2 . Some peculiarities emerge for d ≤ 2 where only an isolated quantum critical point exists. For d > 2 the phase boundary and crossover lines are determined and the physics of the various regions of the phase diagram is found to be consistent with recent renormalization group results. Moreover, for 2 d 4 the crossovers near criticality are suitably described in terms of scaling functions and effective critical exponents.

Reply to French and Hussey: Evidence against orbital origin of field-induced quantum criticality in Tl 2 Ba 2 CuO 6+ x superconductors

In our recent article (1), we reported recovering Fermi-liquid features through quantum critical behavior in Tl2Ba2CuO6+x at high magnetic fields. French and Hussey (2) propose an alternative explanation for our results based entirely on orbital effects, assuming a temperature-dependent anisotropy of ωcτ in the basal plane. Their simulations show slight deviations in the Kohler's plot in their figure 1D. However, when compared with our experimental data (see Fig. 1) their extent of apparent violation is much smaller. This huge difference provides compelling evidence that the orbital origin cannot explain our experimental observations quantitatively.

Field-induced multiple-point quantum criticality in the three-leg Heisenberg ladder

Field-induced quantum (zero temperature) criticality described using parameters that are not associated with a symmetry-breaking long-range order is found in the spin-$\frac{1}{2}$ antiferromagnetic three-leg Heisenberg ladder. These parameters represent the spin bond order, which is a consequence of the probability for spins on adjacent sites to be bound in a singletlike arrangement. They underwent two phase transitions, one at the lower critical field ${h}_{c1}$ and the other at the upper critical field ${h}_{c2}$. The field dependence of these bond parameters and of the magnetization is calculated for several values of the rung coupling in all regimes. This yields the coupling field phase diagram. It is found that the rung coupling must exceed a threshold value for the plateau, at one third of the saturation magnetization, to appear. The results obtained here within the bond mean-field theory compare well with existing numerical data.

Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

In high-transition-temperature (T(c)) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above T(c), the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T(2)) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a transformation from the non-Fermi-liquid state to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-T(c) superconductor Tl(2)Ba(2)CuO(6+x). From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field that decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field-with the Fermi-liquid coefficient of the T(2) dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two-dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations.

Field-induced quantum criticality in YbAgGe

YbAgGe is one of the very few stoichiometric, Yb-based, heavy fermion materials that exhibit field-induced quantum criticality. We will present an overview of thermodynamic and transport measurements in YbAgGe single crystals. Moderate magnetic field (45–90 kOe, depending on orientation) suppresses long range magnetic order, giving rise to non-Fermi-liquid behavior followed at higher field by a crossover to a heavy Fermi-liquid. Given the more accessible temperature and field scales, a non-Fermi liquid region rather than point for T → 0 K may be detected.