Metamagnetic Quantum Critical End Point Research Articles

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.

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.

Pressure study of nematicity and quantum criticality in Sr3Ru2O7for an in-plane field

We study the relationship between the nematic phases of Sr$_3$Ru$_2$O$_7$ and quantum criticality. At ambient pressure, one nematic phase is associated with a metamagnetic quantum critical end point (QCEP) when the applied magnetic field is near the \textit{c}-axis. We show, however, that this metamagnetic transition does not produce the same nematic signatures when the QCEP is reached by hydrostatic pressure with the field applied in the \textit{ab}-plane. Moreover, a second nematic phase, that is seen for field applied in the \textit{ab}-plane close to, but not right at, a second metamagnetic anomaly, persists with minimal change to the highest applied pressure, 16.55 kbar. Taken together our results suggest that metamagnetic quantum criticality may not be necessary for the formation of a nematic phase in Sr$_3$Ru$_2$O$_7$.

Quantum criticality in itinerant metamagnets

Critical thermodynamics close to a metamagnetic quantum critical end point (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 Gr\"uneisen parameter are determined, and the crossover lines in the $(H,T)$ phase diagram are specified. We point out that the metamagnetic QCEP is intrinsically unstable with respect to a magnetoelastic coupling.

Symmetry-Breaking Lattice Distortion inSr3Ru2O7

The electronic nematic phase of Sr₃Ru₂O₇ is investigated by high-resolution in-plane thermal expansion measurements in magnetic fields close to 8 T applied at various angles Θ off the c axis. At Θ < 10° we observe a very small (10⁻⁷) lattice distortion which breaks the fourfold in-plane symmetry, resulting in nematic domains with interchanged a and b axis. At Θ ≳ 10° the domains are almost fully aligned and thermal expansion indicates an area-preserving lattice distortion of order 2 × 10⁻⁶ which is likely related to orbital ordering. Since the system is located in the immediate vicinity of a metamagnetic quantum critical end point, the results represent the first observation of a structural relaxation driven by quantum criticality.

Theory of spontaneous Fermi surface symmetry breaking for [formula omitted

We show that many salient features observed around the metamagnetic transition in Sr 3 Ru 2 O 7 are described within a simple model, which considers only an instability of the Fermi surface symmetry breaking (Pomeranchuk instability), without invoking a putative metamagnetic quantum critical end point as usually assumed for this compound. In our model, the Pomeranchuk instability and unconventional, non-Fermi liquid type properties arise due to the tuning of the van Hove singularity of either a majority or a minority spin band to the vicinity of the Fermi energy by a magnetic field. The obtained phase diagram, the metamagnetic transition, and the temperature dependence of the magnetic susceptibility and specific heat show striking similarities to the experimental data.

Alternating-field magnetoresistance measurements on Sr3Ru2O7

We apply an alternating-field (af) magnetoresistance technique to investigate the temperature–field (T–H) phase diagram of the bilayer ruthenate Sr3Ru2O7 in close vicinity of the metamagnetic quantum critical end point. The out-of-phase component of the af magnetoresistance is extremely sensitive to hysteresis effects. Clear peaks are observed when entering the bounded regime at low temperatures. They mark two separate first-order phase transitions ending at 0.7 and 0.45K, respectively. No indication for hysteresis is observed inside the bounded regime.

Thermal Conductivity in the Vicinity of the Quantum Critical End Point inSr3Ru2O7

Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic fields through the quantum critical end point at Hc=7.85 T. A peak in the electrical resistivity as a function of the field was mimicked by the thermal resistivity. In the limit as T-->0 K, we find that the Wiedemann-Franz law is satisfied to within 5% at all fields, implying that there is no breakdown of the electron despite the destruction of the Fermi liquid state at quantum criticality. A significant change in disorder [from rho0(H=0 T)=2.1 to 0.5 microOmega cm] does not influence our conclusions. At finite temperatures, the temperature dependence of the Lorenz number is consistent with ferromagnetic fluctuations causing the non-Fermi liquid behavior as one would expect at a metamagnetic quantum critical end point.

Metamagnetic Quantum Criticality inSr3Ru2O7Studied by Thermal Expansion

We report low-temperature thermal expansion measurements on the bilayer ruthenate Sr3Ru2O7 as a function of magnetic field applied perpendicular to the ruthenium-oxide planes. The field dependence of the c-axis expansion coefficient indicates the accumulation of entropy close to 8 T, related to an underlying quantum critical point. The latter is masked by two first-order metamagnetic transitions which bound a regime of enhanced entropy. Outside this region the singular thermal expansion behavior is compatible with the predictions of the itinerant theory for a two-dimensional metamagnetic quantum critical end point.

Reentrant hidden order at a metamagnetic quantum critical end point.

Magnetization measurements of URu2Si2 in pulsed magnetic fields of 44 T reveal that the hidden order phase is destroyed before appearing in the form of a reentrant phase between approximately 36 and 39 T. Evidence for conventional itinerant electron metamagnetism at higher temperatures suggests that the reentrant phase is created in the vicinity of a quantum critical end point.

Residual resistivity near a two-dimensional metamagnetic quantum critical point

The behavior of the residual (impurity-dominated) resistivity is computed for a material near a two dimensional quantum critical point characterized by a divergent $q=0$ susceptibility. A singular renormalization of the amplitude for back-scattering of an electron off of a single impurity is found. When the correlation length of the quantum critical point exceeds the mean free path, the singular renormalization is found to convert the familiar `Altshuler-Aronov' logarithmic correction to the conductivity into a squared-logarithmic form. Impurities can induce unconventional Friedel oscillations, which may be observable in scanning tunnelling microscope experiments. Possible connections to the metamagnetic quantum critical end point recently proposed for the material $Sr_{3}Ru_{2}O_{7}$ are discussed.

A METAMAGNETIC QUANTUM CRITICAL ENDPOINT IN Sr3Ru2O7

In this paper, we discuss the concept of a metamagnetic quantum critical end-point, consequence of the depression to zero temperature of a critical end-point terminating a line of first order first transitions. This new type of quantum critical point (QCP) is interesting both from a fundamental point of view: a study of a symmetry conserving QCP, and because it opens the possibility of the use of symmetry breaking tuning parameters, notably the magnetic field. In addition, we discuss the experimental evidence for the existence of such a QCP in the bilayer ruthenate Sr3Ru2O7.