Our group investigates fundamental problems in condensed matter physics through massively parallel computation using ISSP supercomputers and “K-computer” at Kobe. For this purpose, we also develop new algorithms. As for quantum critical phenomena, for example, we are trying to find a “deconfined” critical phenomena, a new category of quantum phase transition, as a transition between Neel state and VBS state in the SU(N) Heisenberg model. Another target in this area of research is the existence/absence of super-solid phase in optical lattices and in He4 systems adsorbed on graphite surfaces. As for classical systems, we investigate the phase transition due to the Z2 vortex dissociation, an unconventional critical phenomena caused by the symmetry-breaking dangerously-irrelevant field, etc. Our most recent activities are focused on developments of tensor network methods and their applications to frustrated spin systems.

A super-operator that defines renormalization transformation of two-site operators. Each tensor represented by a polygon is computed through MERA.

Scaling-dimensions obtained by solving the eigenvalue problem of the super-operator.

Research Subjects

Search for novel quantum phases and quantum transitions

Fast Algorithm for Generating Random Bit Strings and Multispin Coding for Directed Percolation: H. Watanabe, S. Morita, S. Todo and N. Kawashima, J. Phys. Soc. Jpn.88 (2019) 024004(8pages).

Calculation of higher-order moments by higher-order tensor renormalization group: S. Morita and N. Kawashima, Computer Physics Communications236 (2019) 65-71.

^{*}SIMD vectorization for the Lennard-Jones potential with AVX2 and AVX-512 instructions: H. Watanabe and K. M. Nakagawa, Computer Physics Communications237 (2019) 1-7.

^{*}A series of magnon crystals appearing under ultrahigh magnetic fields in a kagomé antiferromagnet: R. Okuma, D. Nakamura, T. Okubo, A. Miyake, A. Matsuo, K. Kindo, M. Tokunaga, N. Kawashima, S. Takeyama and Z. Hiroi, Nature Communications10 (2019) 1229(7).