Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSuperconducting gap and vortex lattice of the heavy fermion compound CeCu_2Si_2
194
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The order parameter and pairing mechanism for superconductivity in heavy fermion compounds are still poorly understood. Scanning tunneling microscopy and spectroscopy at ultra-low temperatures can yield important information about the superconducting order parameter and the gap structure. Here, we study the first heavy fermion superconductor, CeCu_2Si_2. Our data show the superconducting gap which is not fully formed and exhibits features that point to a multi-gap order parameter. Spatial mapping of the zero bias conductance in magnetic field reveals the vortex lattice, which allows us to unequivocally link the observed conductance gap to superconductivity in CeCu_2Si_2. The vortex lattice is found to be predominantly triangular with distortions at fields close to sim 0.7 H_{c2}.
rate research
Read More
Anisotropic, spatially textured electronic states often emerge when the symmetry of the underlying crystalline structure is lowered. However, the possibility recently has been raised that novel electronic quantum states with real-space texture could arise in strongly correlated systems even without changing the underlying crystalline structure. Here we report evidence for such texture in the superconducting quantum fluid that is induced by pressure in the heavy-fermion compound CeRhIn5. When long-range antiferromagnetic order coexists with unconventional superconductivity, there is a significant temperature difference between resistively- and thermodynamically-determined transitions into the superconducting state, but this difference disappears in the absence of magnetism. Anisotropic transport behaviour near the superconducting transition in the coexisting phase signals the emergence of textured superconducting planes that are nucleated preferentially along the {100} planes and that appear without a change in crystal symmetry. We show that CeRhIn5 is not unique in exhibiting a difference between resistive and bulk superconducting transition temperatures, indicating that textured superconductivity may be a general consequence of coexisting orders.
The thermal conductivity $kappa$ of the heavy-fermion superconductor CeIrIn$_5$ was measured as a function of temperature down to $T_c$/8, for current directions perpendicular ($J parallel a$) and parallel ($J parallel c$) to the tetragonal c axis. For $J parallel a$, a sizable residual linear term $kappa_0 / T$ is observed, as previously, which confirms the presence of line nodes in the superconducting gap. For $J parallel c$, on the other hand, $kappa / T to 0$ as $T to 0$. The resulting precipitous decline in the anisotropy ratio $kappa_c / kappa_a$ at low temperature rules out a gap structure with line nodes running along the c-axis, such as the d-wave state favoured for CeCoIn$_5$, and instead points to a hybrid gap of $E_g$ symmetry. It therefore appears that two distinct superconducting states are realized in the Ce$M$In$_5$ family.
A Kondo lattice of strongly interacting f-electrons immersed in a sea of conduction electrons remains one of the unsolved problems in condensed matter physics. The problem concerns localized f-electrons at high temperatures which evolve into hybridized heavy quasi-particles at low temperatures, resulting in the appearance of a hybridization gap. Here, we unveil the presence of hybridization gap in Ce2RhIn8 and find the surprising result that the temperature range at which this gap becomes visible by angle-resolved photoemission spectroscopy is nearly an order of magnitude lower than the temperature range where the magnetic scattering becomes larger than the phonon scattering, as observed in the electrical resistivity measurements. Furthermore the spectral gap appears at temperature scales nearly an order of magnitude higher than the coherent temperature. We further show that when replacing In by Cd to tune the local density of states at the Ce3+ site, there is a strong reduction of the hybridization strength, which in turn leads to the suppression of the hybridization gap at low temperatures.
We report a study on the interplay between antiferromagnetism (AFM) and superconductivity (SC) in a heavy-fermion compound CeRhIn$_5$ under pressure $P=1.75$ GPa. The onset of the magnetic order is evidenced from a clear split of $^{115}$In-NQR spectrum due to the spontaneous internal field below the Neel temperature $T_N=2.5$ K. Simultaneously, bulk SC below $T_c=2.0$ K is demonstrated by the observation of the Meissner diamagnetism signal whose size is the same as in the exclusively superconducting phase. These results indicate that the AFM coexists homogeneously with the SC at a microscopic level.
We report on the anisotropic properties of Pauli-limited superconductivity (SC) and antiferromagnetism (AFM) in the solid solutions CeCo(In_{1-x}Zn_x)_5 (x<=0.07). In CeCo(In_{1-x}Zn_x)_5, the SC transition temperature T_c is continuously reduced from 2.3 K (x=0) to ~1.4 K (x=0.07) by doping Zn, and then the AFM order with the transition temperature of T_N~2.2 K develops for x larger than ~0.05. The present thermal, transport and magnetic measurements under magnetic field B reveal that the substitution of Zn for In yields little change of low-temperature upper critical field mu_0H_{c2} for both the tetragonal a and c axes, while it monotonically reduces the SC transition temperature T_c. In particular, the magnitudes of mu_0H_{c2} at the nominal Zn concentration of x = 0.05 (measured Zn amount of ~0.019) are 11.8 T for B||a and 4.8 T for B||c, which are as large as those of pure compound though T_c is reduced to 80% of that for x=0. We consider that this feature originates from a combination of both an enhanced AFM correlation and a reduced SC condensation energy in these alloys. It is also clarified that the AFM order differently responds to the magnetic field, depending on the field directions. For B||c, the clear anomaly due to the AFM transition is observed up to the AFM critical field of ~5 T in the thermodynamic quantities, whereas it is rapidly damped with increasing B for B||a. We discuss this anisotropic response on the basis of a rich variety of the AFM modulations involved in the Ce115 compounds.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
