The Seebeck effect describes the generation of an electric potential in a conducting solid exposed to a temperature gradient. In most cases, it is dominated by an energy-dependent electronic density of states at the Fermi level, in line with the prevalent efforts towards superior thermoelectrics through the engineering of electronic structure. Here we demonstrate an alternative source for the Seebeck effect based on charge-carrier relaxation: a charge mobility that changes rapidly with temperature can result in a sizeable addition to the Seebeck coefficient. This new Seebeck source is demonstrated explicitly for Ni-doped CoSb₃, where a marked mobility change occurs due to the crossover between two different charge-relaxation regimes. Our findings unveil the origin of pronounced features in the Seebeck coefficient of many other elusive materials characterized by a significant mobility mismatch. When utilized appropriately, this effect can also provide a novel route to the design of improved thermoelectric materials.

The low-temperature state of ${\text{CeRu}}_2{\text{Al}}_{10}$ has been studied by neutron powder diffraction and muon spin relaxation. By combining both techniques, we prove that the transition occurring at $T^{\ast }\sim 27\text{K}$, whose origin has been the subject of considerable debate, is unambiguously magnetic due to the ordering of the Ce sublattice. The magnetic structure with a propagation vector of $\mathbf{k}=\left(1,0,0\right)$ involves a collinear antiferromagnetic alignment of the Ce moments along the $c$ axis of the $Cmcm$ space group with a reduced moment of $0.34\left(2\right){\mu }_B$. No structural changes within the resolution limit have been detected below the transition temperature. However, the temperature dependence of the magnetic Bragg peaks and the muon precession frequency show an anomaly around $T_2\sim 12\text{K}$ indicating a possible second transition.

The superconducting state of the newly discovered superconductor ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$, with a quasi-one-dimensional crystal structure $(T_{\mathbf{c}}\sim 6\text{K})$, is investigated using magnetization and muon-spin relaxation or rotation $\left(\mu \mathrm{SR}\right)$ measurements. Our analysis shows that the temperature dependence of the superfluid density obtained from transverse-field $\mu \mathrm{SR}$ measurements fits either to an isotropic $s$-wave character for the superconducting gap or to a $d$-wave model with line nodes. Furthermore, the goodness-of-fit $\left({\chi }^2\right)$ values indicate that our data fit better to the $d$-wave model $\left({\chi }^2\sim 1\right)$ than the $s$-wave model $\left({\chi }^2\sim 1.38\right)$. Therefore our $\mu \mathrm{SR}$ analysis is more consistent with having line nodes than being fully gapped, which is in agreement with the results of the penetration depth measured using a tunnel diode oscillator technique. Our zero-field $\mu \mathrm{SR}$ measurements do reveal very weak evidence of the spontaneous appearance of an internal magnetic field below the transition temperature, which might indicate that the superconducting state is not conventional. This observation suggests that the electrons are paired via unconventional channels such as spin fluctuations, as proposed on the basis of theoretical models of ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$. Furthermore, from our transverse-field $\mu \mathrm{SR}$ study the magnetic penetration depth ${\lambda }_L$, superconducting carrier density $n_s$, and effective-mass enhancement $m^{*}$ have been estimated to be ${\lambda }_L\left(0\right)=432\left(4\right)$ nm, $n_s=2.7\times {10}^{27}\text{carriers}/{\mathrm{m}}^3$, and $m^{*}=1.75m_e$, respectively.

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi${}_3$ by performing magnetization, specific heat, electrical resistivity, and muon spin relaxation ($\mu$SR) measurements. LaRhSi${}_3$ crystallizes with the BaNiSn${}_3$-type tetragonal structure (space group $I4\hspace{0.5em}\mathit{mm}$), as confirmed through our neutron diffraction study. Magnetic susceptibility, electrical resistivity and specific heat data reveal a sharp and well-defined superconducting transition at $T_c=2.16\pm 0.08$ K. The low-temperature specific heat data reveal that LaRhSi${}_3$ is a weakly coupled bulk BCS superconductor and has an $s$-wave singlet ground state with an isotropic energy gap of $~$0.3 meV, $2{\Delta }_0/k_B{T}_c=3.24$. The specific heat data measured in an applied magnetic field strongly indicate a type I behavior. Type I superconductivity in this compound is also inferred from the Ginzburg-Landau parameter, $\kappa =0.25$. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth, and coherence length, characterize LaRhSi${}_3$ as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature ($H-T$) phase diagram is presented and from a consideration of the free energy, the thermodynamic critical field, $H_{c0}$, is estimated to be $17.1\pm 0.1$ mT, which is in very good agreement with that estimated from the transverse field $\mu$SR measurement that gives $H_{c0}=17.2\pm 0.1$ mT. The transverse field $\mu$SR results are consistent with conventional type I superconductivity in this compound. Further, the zero field $\mu$SR results indicate that time-reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi${}_3$.