Expert Profile:

Curriculum Vitae of Dr. Keiji Saito               

Education

1990-1995: Faculty of Science, Kyoto University

1994: Bachelor of Science degree, Kyoto University

1994-1996: Graduate School of Human Environmental Studies, Kyoto University

1996: Master degree of Human Environmental Studies, Kyoto University

1996-1999: Faculty of Science, Osaka University

1999: Ph.D in Physics, Osaka University

Research Careers

1999-2004: Assistant Professor, Department of Applied Physics, University of Tokyo

2004-2012: Assistant Professor, Department of Physics, University of Tokyo

2012-2017: Associate Professor, Department of Physics, Keio University

2017-2023: Professor, Department of Physics, Keio University

2023-present: Professor, Department of Physics, Kyoto University  

Award

Presentation Title:

Energy diffusion in the long-range interacting spin systems

Abstract:

We investigate energy diffusion in long-range interacting spin systems, where the interaction decays algebraically as with the distance r between the sites. We consider prototypical spin systems, the transverse Ising model, and the XYZ model in the D-dimensional lattice with a finite exponent α > D which guarantees the thermodynamic extensivity. In one dimension, both normal and anomalous diffusion are observed, where the anomalous diffusion is attributed to anomalous enhancement of the amplitude of the equilibrium current correlation. We prove the power-law clustering property of arbitrary orders of joint cumulants in general dimensions. Applying this theorem to equal-time current correlations, we further prove several theorems leading to the statement that the sufficient condition for normal diffusion in one dimension is α > 3/2 regardless of the models. The fluctuating hydrodynamics approach consistently explains Lévy diffusion for α <3/2, which implies the condition is optimal. In higher dimensions of D ≥ 2, normal diffusion is indicated as long as α > D.