Slichter Peak Research Articles

Detection of Two Phenomena Opposite to the Expected Ones

Both phenomena mentioned in the title were revealed by the electron paramagnetic resonance (EPR) method. The first phenomenon was found in superconducting La metal with Er impurities—the spin relaxation rate of the erbium impurities was sharply decreasing after transition into the superconducting state instead of the expected, i.e., the well-known Hebel–Slichter peak. The second unexpected phenomenon was discovered in the YbRh2Si2 compound—an excellent EPR signal from the Yb ions was observed at temperatures below the Kondo temperature determined thermodynamically, while according to the existing belief the EPR signal should not be observed at these temperatures due to the Kondo effect. In this tribute to K. Alex Müller, I describe the nature of the detected phenomena.

NMR diagnosis of pseudo-scalar superconductivity in 3D Dirac materials

Recently observed 4π periodic Andreev bound states in 3D Dirac materials are attributed to conventional superconducting pairing. Our alternative explanation in terms of a novel form of parity breaking pseudo-scalar superconducting order can be sharply diagnosed by nuclear magnetic resonance relaxation rate. The left–right symmetry breaking of the pseudo-scalar superconductivity can be directly probed as an anti-peak structure below TC in sharp contrast to the conventional Hebel–Slichter peak.

75As-NQR Investigation of the Relationship between the Instability of Metal–Insulator Transition and Superconductivity in Ru1−xRhxAs

We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution region and the critical fluctuations seen in the nuclear spin–lattice relaxation rate at the metal–insulator transition of RuAs. The critical fluctuation at TMI1 ∼ 255 K for RuAs is suppressed by the Rh substitution, and superconductivity with the maximum transition temperature is realized in the region where critical fluctuations are weakened significantly. The nuclear spin–lattice relaxation rate exhibits a Hebel–Slichter peak together with typical metallic behavior, demonstrating that superconductivity with a conventional s-wave character is realized without remarkable development of magnetic or electric fluctuations in Ru1−xRhxAs.

Nuclear spin-lattice relaxation rate in electron-doped Pr 0.91LaCe 0.09CuO 4 − y: Constraint on the gap symmetry

We present numerical calculations of the nuclear spin-lattice relaxation ( R s ) rate in the superconducting state of pure indium and slightly underdoped n-type cuprate Pr 0.91LaCe 0.09CuO 4 − y . By properly taking into account electron–phonon coupling, our calculated R s for the conventional s-wave superconductor, indium, is in quantitative agreement the experimental data with a clear Hebel–Slichter peak. In contrast, the absence of the Hebel–Slichter peak in the R s data of Pr 0.91LaCe 0.09CuO 4 − y can be explained by either d-wave or highly anisotropic s-wave gap symmetry. Thus, the absence of the Hebel–Slichter peak does not necessarily argue against an s-wave gap symmetry in this electron-doped cuprate.

DC-magnetization and 1H-NMR studies of layered superconductor Li0.48(THF)0.3HfNCl

DC-magnetization and 1H-NMR measurements were carried out on a layered superconductor Li0.48(THF)yHfNCl (Li–HfNCl) having a relatively high Tc of 25.5K. A drastic enhancement of 1H-NMR relaxation rate 1/T1 in the superconducting state was observed in highly oriented Li–HfNCl pellets, where the temperature dependence of 1/T1 has a peak around 7–10K well below Tc(H). This behavior cannot be explained by the “Hebel–Slichter peak” for conventional BCS superconductors. Magnetization measurements revealed reversible behaviors in the temperature range from Tc to Tirr. These unusual behaviors are explained by the vortex dynamics inherent in the layered superconductors.

Nuclear magnetic relaxation in YNi 2− xPt xB 2C

The temperature dependence of 13C spin-lattice relaxation time T 1 in YNi 2− x Pt x B 2C ( x=0 and 0.8) has been measured. With decreasing temperature the relaxation rate 1/ T 1 forms a Hebel–Slichter peak just below T c and after that it decreases exponentially with the gap parameter 2Δ 0=4.8 k B T c . Below about 4 K it starts to vary linearly with T, where the values of 1/ T 1 T were proportional to H 0, the observing magnetic field. This means that the spin diffusion to normal cores is important for the relaxation. These results support the model of the phonon-mediated superconductivity in this system.

11B and 13C NMR studies of borocarbide superconductor YNi 2B 2C

We have carried out the measurements of the nuclear spin-lattice relaxation rate, ( T 1) −1, of 11B in YNi 2B 2C, Y(Ni 0.8Co 0.2) 2B 2C and Y(Ni 0.7Co 0.3) 2B 2C and of 13C in YNi 2B 2C in a wide temperature range. In the normal state, ( T 1 T) −1 increases with decreasing temperature presumably due to the antiferromagnetic spin fluctuations. ( T 1) −1 in the superconducting state decreases rapidly with decreasing temperature with no Hebel–Slichter peak just below T c. On further decreasing the temperature, ( T 1) −1 decreases linearly with temperature. Such behavior of ( T 1) −1 shows the possibility of unconventional superconductivity, such as d-wave superconductivity in high- T c cuprates.

NMR evidence of BCS superconductivity in Y(Ni 1− xPt x) 2B 2C

13 C and 11 B NMR studies have been made on the quaternary superconductor Y(Ni 1− x Pt x ) 2B 2C with x=0 and 0.4. Temperature dependence of Knight shift and spin-lattice relaxation rate (SLRR) in the normal state was explained consistently among all the observed nuclei by Korringa mechanism without taking account of antiferromagnetic spin fluctuation. Bellow the superconducting transition temperature we observed a Hebel–Slichter peak in case of 13 C SLRR. These results mean that the borocarbide is a normal metal and a phonon-mediated superconductor

Formula omitted] NMR OF YNi 2B 2C SINGLE CRYSTAL IN THE SUPERCONDUCTING STATE

We have measured the spin-lattice relaxation rate 1/ T 1 in an as-grown single crystal of YNi 2B 2C ( T c=13.8 K) in the superconducting state down to 0.9 K. 1/ T 1 shows no Hebel–Slichter peak just below T, decreasing sharply as T 3, and followed by a slow dependence of 1/ T 1∝ T at low temperatures. The pairing state is discussed on the basis of T 1 result.

Korringa relation and Hebel–Slichter peak in ammonia intercalated fullerides by [formula omitted] NMR

The compound (NH 3) x NaRb 2C 60 has been studied by SQUID magnetometry, 23 Na and 1 H NMR. A 23 Na/ 1 H double irradiation NMR experiment evidences a close distance between Na ions and ammonia, confirming the octahedral occupancy of this cluster which is usually observed in the ammonia intercalated fullerides. The Knight shift interaction of the ammonia protons with the conduction electrons is of pure anisotropic nature and is detected as a field dependent broadening of the 1 H NMR lines at low temperature. The recovery of the proton magnetisation follows a single exponential at all the investigated temperatures and fields. A Korringa behaviour is observed below 65 K and a clear Hebel–Slichter coherence peak is detected just below T c. The Korringa relation does not hold and the Knight shift enhancement suggests the presence of a Coulomb repulsion.

The nuclear spin relaxation rate for clean quasi-two-dimensional superconductors in the vicinity of

We calculate the nuclear spin relaxation rate of clean quasi-two-dimensional (2D) superconductors with s-wave pairing in high magnetic fields using the BCS model and the Brandt, Pesch and Tewordt approximation for the single-particle propagator. The calculation is valid in the vicinity of . Thermal fluctuations of vortices are not taken into account. We evaluate numerically our results in the case of high- materials and organic superconductors. In a perpendicular field the Hebel - Slichter coherence peak is suppressed depending on the variation of the quasi-particle lifetime below . We also describe the magnetic field dependence of the nuclear spin relaxation rate. Using the experimentally determined value of the quasi-particle lifetime, the model reproduces the experimental initial variations of versus at different magnetic fields. However, the Hebel - Slichter peak is conserved in the low-field limit, or when the applied magnetic field is parallel to the superconducting planes.