Monoclinic semimetal IrSi synthesized under high pressure above 25 GPa: Crystal structure, electronic, and magnetic properties

We have synthesized a monoclinic phase of IrSi by means of high-pressure and high-temperature treatment above 25 GPa, whereas the theoretically predicted high-pressure phase (i.e., FeSi-type structure) was not identified up to 48 GPa. Magnetotransport measurements clarify the semimetallic nature (carrier density of $\sim 6-9\times {10}^{19}/\mathrm{c}{\mathrm{m}}^3$) of monoclinic IrSi, in agreement with our band structure calculations. Furthermore, the surface electronic bands are predicted to show the large Rashba spin splitting, offering potential spintronic applications of this material.

Figure 1

Powder x-ray diffraction pattern for the arc-melted sample (a) and the sample synthesized at 25 GPa and 800 °C (c). The result of Reitveld refinement is also shown for (c), with the background intensity subtracted from the data. The refined crystal structures are shown in (b) and (d), respectively.

Figure 2

(a) Volume dependence of the internal energy calculated for the orthorhombic (Pnma) phase (blue circles), monoclinic ($P{2}_1/c$) phase (red squares), and the previously predicted cubic (ε-FeSi-type) phase [15] (green diamonds). The solid lines are the corresponding equations of state $E$($V$) for these phases obtained by fitting the calculated results to the third-order Birch-Murnaghan equation. $V_0$ is the volume of the orthorhombic unit cell at the ambient pressure. (b) A magnified view of the equation of states. The resulting common tangent between the orthorhombic and monoclinic (cubic ε-FeSi-type) phases is shown by the black dashed line (grey dash-dotted line). Here, $P_{\mathrm{OM}}$ ($P_{\mathrm{OC}}$) is the negative slope of the common tangent and corresponds to the pressure needed for the transition from orthorhombic to monoclinic (cubic) phase. (c) The pressure dependence of the enthalpy difference between the orthorhombic and monoclinic phase (black dashed line), compared against that between the orthorhombic and cubic phase (grey dash-dotted line).

Figure 3

Brillouin Zone (a), band structure (b), and density of states (DOS) (c) for the monoclinic IrSi. The surface projection of $k$ points is denoted by the green dots in (a).

Figure 4

Magnetic and electronic properties of monoclinic IrSi. (a). Temperature dependence of magnetic susceptibility measured at a magnetic field of $B=7\mathrm{T}$. (b) Temperature dependence of resistivity measured at $B=0\mathrm{T}$. (c) Hall resistivity measured at various temperatures. (d) Temperature dependence of carrier density $n$ and mobility μ.

Figure 5

Surface band structure of monoclinic IrSi showing large Rashba spin splitting. The definition of $k$ points is shown in Fig. 3.