Transport phenomena in fractionalized quantum materials

Abstract

The quantum effects in a many-body system can induce novel behavior on a system with fractionalized degrees of freedom, whose study is not only interesting from the perspective of fundamental research but also in view of potential applications to quantum technologies such as quantum computers. In this regard, quantum spin liquids are systems of particular interest. They are an exotic phase of matter characterized by the presence of fractionalized excitation (spinons) and emergent gauge fields. The efforts in the community have not yet succeeded in asserting the existence of quantum spin liquids beyond any reasonable doubt. The technological advances in material synthesis provide us with two-dimensional samples of candidate quantum spin liquid materials like 1T-TaS2, 1T-TaSe2, and αRuCl3, which might avoid the problem of the disruptive effects of the interlayer interactions in candidate materials. Experimental techniques like neutron scattering, aimed at measuring the bulk properties of a sample, are not applicable in the case of two-dimensional samples. One of the difficulties in probing experimentally a QSL phase comes from the fact that the spinons do not carry an electric charge, ruling out the possibility of using conventional electrical probes. Going beyond conventional transport, we propose two setups of electric probes to characterize a QSL phase. First, we analyze a setup in which a QSL layer is interposed between two metallic layers. In this setup, we apply a current in the first metallic layer and measure the induced voltage on the second one. The momentum transfer is affected by the non-trivial behavior of momentum-carrying spinons and results in a response that carries information about the dynamic of the spinons and will potentially be helpful for the future characterization of candidate QSL materials. The second probe we propose is a scanning tunneling microscopy (STM) experiment on a Kondo lattice with the addition of an antiferromagnetic interaction between the localized magnetic moments. We calculate the STM response in each of the phase configurations of this system allowing also for the possibility for the conduction electrons and for the spinons to form a superconducting phase and present our derivation of the mean field equations in a Kondo lattice system. This last setup might find a concrete realization in materials such as TaS2, TaSe2, and NbSe2 in the 1T, 2H, and in the 4Hb crystallographic phases.