Quantum Phase Transition in Partially Cu-Doped ZrNi2-xCuxGa Heusler Alloys

Abstract

Quantum phase transition (QPT) is a 2nd order solid state phase transition that starts at a quantum critical point (QCP) and continues to 0 K. Since all thermal fluctuations are absent at 0 K, QPT is caused by strong quantum fluctuations1. Since the lowest measuring temperature that can be experimentally reached in a research laboratory is between 20 mK and 50 mK, the QCP is generally determined by performing an extrapolation of the experimental data points (to 0 K) in the p vs. T (p is the control parameter and T is the temperature) phase diagram. ZrNi2Ga is a superconductor and belongs to the Ni-based Heusler family. The material exhibits a superconducting phase transition at ~2.9 K.2 When Ni is partially replaced by Cu in ZrNi2-xCuxGa the transition temperature linearly decreased to 1.85 K for x = 0.25.3 This is indicative of QPT in the system. Here, we have studied the magneto-transport properties of ZrNi2-xCuxGa (0.25 < 0 ≤ 0.5) to further explore the possible QPT in the system. The samples were prepared by arc melting and the transport measurements were done on a Physical Property Measurement system with Helium-3 attachment. All samples exhibited the L21 cubic structure at room temperature. A superconducting phase transition temperature of as low as ~1 K was observed in the system, which nearly confirms the possibility of QPT in the ZrNi2-xCuxGa system. The experimental results will be presented in details.