"How electron decides its direction in a solid: going left or right?" Masafumi Udagawa

Theory of Quantum Matter Unit would like to invite you to a seminar :

• Speaker: Dr. Masafumi Udagawa, Research Associate at Department of Applied Physics, University of Tokyo
• Date/Time: Mon 28th October / 10:30-11:30am
• Venue: C016, Level C, Lab 1

How electron decides its direction in a solid: going left or right ?

– Spin scalar chirality and topological Hall effect in spin ice –

Masafumi Udagawa

Department of Applied Physics, University of Tokyo

Hall effect is one of the most fundamental transport phenomena in solid. Under a magnetic field, current flows in a transverse direction to the applied electric field. Magnetic field affects the quantum-mechanical phase of electronic wave function and as a result, shifts their position in real space, as is clearly demonstrated in the classical experiment of Aharonov-Bohm effect.

Recently, a remarkable proposal has been made as to a new possible origin of the Hall effect. The spin scalar chirality, associated with a triplet of magnetic moments, can be a driving force to bend the trajectory of electrons in a similar way to magnetic field [Fig. 1(a)]. This proposal opens a door to the new possibility of non-trivial transport in frustrated magnets, where magnetic order sometimes accompanies finite spin scalar chirality.

We pursue this possibility in a representative example of frustrated magnet, spin ice [Fig.1(b)]. For this purpose, we focus on Pr2Ir2O7, where itinerant electrons of Ir 5d orbitals interact with spin ice formed by Pr 4f localized electrons. We examine how spin scalar chirality associated with spin ice affects the Hall response, and as a result, we could successfully reproduce the experimental Hall conductivity of Pr2Ir2O7 [1,2]. The obtained Hall conductivity possesses several conspicuous features: [111] peak and sign reversal, which can be interpreted in terms of characteristic behaviors inherent in spin ice: spin-ice-kagome-ice crossover, and liquid-gas crossover of monopoles [Fig. 1(c)].

[1] Y. Machida et al., Phys. Rev. Lett. 98, 057203 (2007). 

[2] M. Udagawa and R. Moessner, Phys. Rev. Lett., 111, 036602 (2013).

(a) Schematic figure of spin triplet spanning finite spin scalar chirality χT. (b) An example of spin ice configuration. (c) The obtained result of Hall conductivity for Pr2Ir2O7.