Three Magnetization Peaks in HgBa$_2$Ca$_2$Cu$_3$O$_8$ Single Crystals

Abstract

By measuring magnetization hysteresis loops of the superconducting HgBa$_2$Ca$_2$Cu$_3$O$_8$ single crystals ($T_{\rm c}$ = 133 K), we observed three magnetization peaks in a wide temperature region. This is in contrast to the previous observation that there are only two magnetization peaks in many superconductors. Detailed analysis finds that the second peak here evolves from a kinky structure at low temperatures and gets enhanced at high temperatures; the third peak evolves from a general broad peak at low temperatures and evolves into a sharp peak and even a step-like one at high temperatures. We propose a general phase diagram to interpret these peaks, the second peak is corresponding to the order-disorder transition, while the third peak is associated with the elastic-plastic crossover. Our work unifies the understanding of different "second peak" structures in different systems and thus sheds new light in understanding the vortex dynamics in type-II superconductors.

Figures (5)

• Figure 1: Main panel: Temperature dependence of the in-plain resistivity of a HgBa$_2$Ca$_2$Cu$_3$O$_8$ single crystal at zero magnetic field. The bottom-right inset gives an enlarged view of resistivity data near $T{\rm_c}$. The upper-left inset shows the temperature dependence of the magnetization of HgBa$_2$Ca$_2$Cu$_3$O$_8$ single crystal under a magnetic field of 10 Oe measured in zero-field-cooling (ZFC) and field-cooling (FC) modes.
• Figure 2: (a)$-$(d) Isothermal magnetic hysteresis loops of a HgBa$_2$Ca$_2$Cu$_3$O$_8$ single crystal for $H \parallel c$. Temperatures are indicated in each panel. The inset in (d) shows an enlarged view of magnetization in the temperature region from 100 K to 115 K where the third peak gets into a step-like structure and eventually vanishes at higher temperatures. All MHLs shown here were measured with ${\rm d} H/{\rm d}t = 50$ Oe/s.
• Figure 3: (a)$-$(d) Magnetic field dependence of transient superconducting current density $J_s$ derived from the Bean critical state model from Fig.\ref{['fig2']} in a semi-log plot for temperatures $T$ = 10$-$45 K(a), $T$ = 50$-$80 K(b), $T$ = 85$-$115 K(c). The arrows indicate positions of $H_{\rm kink}$, $H_{\rm p2}$, $H_{\rm p3}$, respectively. The panel (d) shows the $J_{\rm s}(H)$ curves at high temperatures using linear coordinates. Estimation of $H_{\rm kink}$ is show in panel (a) and (b).
• Figure 4: Field dependence of transient superconducting current density $J_{\rm s}(H)$ with ${\rm d} H/{\rm d}t =$ 50 Oe/s (solid) and 200 Oe/s (open) and dynamic magnetic relaxation rate $Q(H)$ at 60K, 70K, and 85K. Two vertical dashed lines indicate the positions of $Q_{\rm min1}$ and $Q_{\rm min2}$ for 85K.
• Figure 5: Vortex phase diagram of HgBa$_2$Ca$_2$Cu$_3$O$_8$ single crystal with $H \parallel c$ in a semi-log plot, depicted from the results of magnetization measurements and dynamic magnetic relaxation rate measurements. The transition lines $Q_{\rm min1}$(square) and $H_{\rm p3}$(down triangle) separate the vortex solid into three parts. ).