Search for superconductivity in CrB 2 under pressure 29A13025 Shimizu Lab Kaide Naohiro

Contents Superconductivity CrB 2 Discussion Summary & Future work

What is “superconductivity” ? conductors-and-the-valence-band/ 1.zero electrical resistance 2.Meissner effect 3.Josephson effect 1.1. Ｔ c = 4.2 K 2.2.

The history of superconductors

Table of AlB 2 structure

CrB 2 1. a hexagonal layer structure (AlB 2 structure) C. Michioka et al., J. Mag. Mat.,310 (2007) 620.

2. Itinerant antiferromagnet 遍歴反強磁性 SDW(spin density wave) スピン密度波 λ = n ・ a n : integer multiple ・・・ “commensurate （整合） ” n : not integer multiple ・・・ “incommensurate （不整合） ” CrB 2

paramagnetic antiferromagnetic Neel temperature (T N ) : The temperature at which “paramagnetic” changes to “antiferromagnetic” T < T N T > T N CrB 2 3. T N =88 K

Temperature dependence of electrical resistivity (CrB 2 ) ・ The resistivity displays a kink at the T N Takaho tanaka et al, journal of the Less-Common metals, 50 (1976) Ambient pressure

Motivation Apply pressure and research for superconductivity

DAC (Diamond anvil cell) Why use Diamond? Hard Transparent 3 cm 6 cm Diamond Anvil Cell (DAC)

Setting ruby pressure medium (Glycerin) 800 μm SUS310S ・ sample: CrB 2 ・ diameter of diamond : 800μm ・ gasket : SUS310S ・ diameter of hole : 200 μm ・ pressure medium ： Glycerin sample diamond Pt Au wire Ruby

order disorder P, B, x T (K) P, B, x : pressure, magnetic field, chemical substitution Quantum critical point ( 量子臨界点 ) Quantum critical point 0

CrB 2 A hexagonal layer structure itinerant antiferromagnetism (T N =88 K) C. Michioka et al., J. Mag. Mat.,310 (2007) 620.

antiferromagnet paramagnet TNTN 0 P (GPa) T (K) PCPC pressure-temperature phase diagram of CrB 2 Researching for superconductivity in CrB 2 around the QCP Quantum critical point

Summary & future work ・ CrB 2 : AlB 2 structure (MgB 2 ), antiferromagnet ・ apply pressure and search for superconductivity around QCP

熱放出 Ruby fluorescence technique

RAMAN

How to estimate pressure Ruby produces fluorescence when irradiated by laser. The wavelength of the peak changes with pressure. For P < 100 GPa : Ruby Fluorescence （ルビー蛍光 法） For P > 100 GPa : Raman Spectroscopy ( ラマン分光法） P = ν ×10 -4 ν 2 Irradiate diamond with laser. On applying pressure, the vibration of C-C bond in diamond changes, the wavelength of scattered light becomes small.

Why high T C is necessary ? critical current – critical temperature - critical magnetic field phase diagram O.K. around 20 K !! MgB 2 Research towards utilization Wire rod