Superconductivity in multiple phases of compressed GeSb2Te4

Abstract

Here we report the discovery of superconductivity in multiple phases of the compressed GeSb2Te4 (GST) phase change memory alloy, which has attracted considerable attention for the last decade due to its unusual physical properties with many potential applications. Superconductivity is observed through electrical transport measurements, both for the amorphous (a-GST) and for the crystalline (c-GST) phases. The superconducting critical temperature, TC, continuously increases with the applied pressure reaching a maximum Tc =6K at P=20 GPa for a-GST, whereas the critical temperature of the cubic phase reaches a maximum Tc =8 K at 30 GPa. This new material system, exhibiting a superconductor-insulator quantum phase transition (SIT) has an advantage over disordered metals since it has a continuous control of the crystal structure and the electronic properties using pressure as an external stimulus, which was lacking in SIT studies until today.

Superconductor-insulator transition in fccGeSb2Te4at elevated pressures

“…The observed coexistence of both phases throughout a wide range of pressures is most probably due to inhomogeneous pressure distribution inside the cell (Al2O3+NaCl is considered a poor pressure medium relative to Ne which is used for XRD measurements). We associate the higher Tc value with b-GST, since it is apparent that the critical temperature of a'-GST has already been saturated at about 6.6 K and the higher value for b-GST is consistent with our previously reported results for this phase [11]. …”

“…Initially, the few micron thick GST films were sputtered from a commercial target of h-GST (hexagonal GeSb2Te4). As we reported earlier [11], the films sputtered onto a room temperature substrate are amorphous (a-GST). An atomic composition and morphology of the as-prepared a-GST film was checked by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analysis [11].…”

“…One of the newly discovered properties of the GST is the emergence of the superconductivity under elevated pressures [11]. In our previous highpressure study of GST [11], superconductivity was observed in amorphous GST (a-GST), orthorhombic GST (o-GST) and in bcc GST (b-GST).…”

“…One of the newly discovered properties of the GST is the emergence of the superconductivity under elevated pressures [11]. In our previous highpressure study of GST [11], superconductivity was observed in amorphous GST (a-GST), orthorhombic GST (o-GST) and in bcc GST (b-GST). In addition we have demonstrated [11] that hexagonal GST remained in the normal state for the entire range of available temperatures and pressures.…”

Multiple phase transitions in Sc doped Sb2Te3 amorphous nanocomposites under high pressure

“…Realizing improved trade-off between crystallization speed (writing) and amorphous phase stability (data retention) remains a challenging issue in PCM. Over the past few decades, amorphous Ge 2 Sb 2 Te 5 and Ge 1 Sb 2 Te 4 (both referred to as GST in this Letter) have received much attention as the matured PCMs, [2][3][4][5][6][7] but are still limited by the tens of nanoseconds writing speed due to the stochastic crystal nucleation during crystallization. Prototypical amorphous Sb 2 Te 3 shows a more rapid crystallization rate than GST at high temperature but has poor thermal stability at room temperature.…”