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1
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Strong-Coupling Features in YB_6 and ZrB_{12} Studied by Point-Contact Spectroscopy

100%
Girovský J., Szabó P., Mori T., Samuely P.
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issue 5
1042-1044
EN
Point-contact spectroscopy studies of the superconducting energy gap and the electron-phonon coupling mechanism are performed on the boron rich YB_6 and ZrB_{12} single crystals. The obtained values of the superconducting energy gaps suggest the strong coupling with 2 Δ/k_{B}T_{c}≈ 4.2 for YB_6 and 2 Δ/k_{B}T_{c}≈ 4.15 for ZrB_{12}. We have observed the dominant soft phonon modes mediating superconductivity in the both samples at energy ≈ 8 meV for YB_6 and ≈ 11 meV in ZrB_{12}, respectively.
2
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Superconductivity Near Transition to Insulating State in MoC Ultrathin Films Studied by Subkelvin STM

88%
Szabó P., Neilinger P., Trgala M., Grajcar M., Samuely P.
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vol. 126
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issue 1
368-369
EN
We study the homogeneously disordered MoC thin films with thicknesses of 10 and 5 nm and the superconducting transition temperatures near 6 and 4 K, significantly decreased as compared to the bulk T_{c}=8.32 K due to a disorder. The scanning tunnelling spectroscopy reveals in the thicker sample a BCS superconducting energy gap Δ with a broadening parameter Γ equal to about 10 per cent of Δ. Remarkably, Γ increases with temperature. The thinner, more disordered sample shows a gapped superconducting density of states but without any coherence peaks at the gap edge, which could not be approximated by the BCS DOS. Moreover, the reduced DOS around the Fermi level persists above the resistive transition temperature reminding the pseudo-gap known from high-T_{c} cuprates.
3
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Specific Heat Study of Superconductivity in Cu_{0.061}TiSe_{2}

76%
Kačmarčík J., Pribulová Z., Pal'uchová V., Husaníková P., Karapetrov G., Komanický V., Samuely P.
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vol. 126
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issue 1
322-323
EN
In TiSe_{2} a charge-density-waves order is continuously suppressed by copper doping and superconductivity appears. We report a calorimetric study performed on the superconducting single crystal of Cu_{0.061}TiSe_{2} with T_{c}=2.8 K, measured by the ac technique at low temperatures down to 0.6 K and magnetic fields up to 2 T. Sharp specific heat anomaly at the superconducting transition is found. The temperature dependence of the electronic specific heat and the angular dependence of the critical temperature, measured at a fixed magnetic field, consistently indicate on the existence of a single s-wave superconducting gap with a coupling strength of 2Δ/k_{B}T_{c}=3.6, close to BCS limit.
4
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Phase Diagram of TmB_4 Probed by AC Calorimetry

76%
Kačmarčík J., Pribulová Z., Gabáni S., Samuely P., Siemensmeyer K., Shitsevalova N., Flachbart K.
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issue 5
903-904
EN
TmB_4 is a frustrated system based on the Shastry-Sutherland lattice that exhibits complex magnetic properties. In this contribution the magnetic field B vs. temperature T phase diagram of TmB_4 has been studied by ultrasensitive AC calorimetry in the temperature range between 2.9 and 12 K and in magnetic fields up to 8 T. Apart from already known phases our measurements have recognized several new phase transitions suggesting that the phase diagram of TmB_4 is even more complex and deserves further studies.
5
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Enhanced Superconductivity in Nanosized Tips of Scanning Tunnelling Microscope

76%
Samuely T., Szabó P., Komanický V., Rodrigo J., Vieira S., Samuely P.
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issue 5
1038-1039
EN
Nanosized Pb junctions exhibit superconducting correlations at magnetic fields more than an order of magnitude higher than the zero-temperature critical field of the bulk Pb. The strongly enhanced critical field is a spectacular demonstration of nanosize effect where the Meissner screening currents become ineffective for junction's tip smaller than the London penetration depth (32 nm for Pb). From the enhanced critical field we characterize the geometry of a particular junction using the variable radius pair breaking theoretical model of Suderow et al.
6
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Point Contact Spectroscopy Measurements of Ba(Fe_{0.96}Co_{0.04})_2As_2 Single Crystals

76%
Szabó P., Girovský J., Pribulová Z., Samuely T., Bud'ko S., Canfield P., Samuely P.
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issue 5
1045-1046
EN
Point contact spectroscopy results are presented on the electron underdoped Ba(Fe_{0.96}Co_{0.04})_2As_2 single crystals. Two superconducting energy gaps with coupling values 2 Δ_1 ∿ kT_{c} ≈ 2.55 and 2 Δ_2 ∿ kT_{c} ≈ 11 at T_{c} = 15.5 K have been observed in the point contact spectra. The temperature dependence of the normal state background of the point contact spectra observed between T_{c} and T_{N} indicates antiferromagnetic origin of the V-shaped minimum at zero bias.
7
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Two-Gap Superconductivity in 2H-NbS_2

64%
Pribulová Z., Leroux M., Kačmarčík J., Marcenat C., Klein T., Rodière P., Cario L., Samuely P.
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issue 5
1024-1025
EN
We performed specific heat measurements of the superconducting single crystal of 2H-NbS_2 in the temperature range down to 0.6 K and magnetic fields up to 14 T. The temperature and magnetic field dependence of the electronic specific heat consistently indicate existence of two superconducting energy gaps in the system. The superconducting anisotropy depends on both temperature and magnetic field. Moreover, the angular dependence of the upper critical field deviates from the Ginzburg-Landau behavior and rather reminds that of MgB_2. All these features point to a multigap superconductivity in 2H-NbS_2. Our measurements are in a perfect agreement with the previous scanning tunneling spectroscopy of Guillamón et al.
8
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Influence of Pressure on Superconductivity in YB_{6}

64%
Gabáni S., Pristáš G., Takáčová I., Flachbart K., Gažo E., Mori T., Braithwaite D., Samuely P.
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vol. 126
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issue 1
340-341
EN
Magnetoresistivity measurements on a superconducting system of YB_{6} (T_c ≈7.5 K) down to 60 mK at hydrostatic pressures up to 47 kbar are presented. The superconducting transition temperature, as well as the third critical field H_{c3} reveal a linear decrease with increasing pressure with slopes of d ln H_{c3}/dp=-1.1 %/kbar, and d ln T_c/dp=-0.59 %/kbar. From the latter a critical pressure, p_c ≈ 170 kbar, at which T_c vanishes, is determined.
9
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Local Magnetometry of Cu_{0.064}TiSe_{2}

64%
Pribulová Z., Medvecká Z., Kačmarčík J., Komanický V., Klein T., Husaníková P., Cambel V., Šoltýs J., Karapetrov G., Samuely P.
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vol. 126
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issue 1
370-371
EN
Local magnetometry using miniature Hall-probe array was used to study vortex distribution in superconducting single crystal of Cu_{x}TiSe_{2}, with x=0.064 and T_{c}=3.2 K. We show that vortices after penetration into the sample move towards the center, resulting into a dome-shape field profile. Such a profile is a signature of relatively low pinning. We show that these measured profiles are consistent with a model proposed for the samples in the absence of bulk pinning. Modifications necessary to obtain quantitative agreement between the model and the data are presented.
10
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AC Microcalorimetry of Superconducting MgCNi_3 Single Crystals

64%
Kačmarčík J., Pribulová Z., Samuely P., Marcenat C., Klein T., Jang D., Lee H., Lee H., Lee S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
363-366
EN
The low-temperature specific heat of single-crystal samples of superconducting MgCNi_3 with typical dimensions 200 μm were measured for the first time. A computer controlled ac microcalorimeter using an optical fiber and an infrared light-emitting diode as the heat source was used down to 2 K at magnetic fields up to 8 T. The specific heat data suggest a moderate coupling in MgCNi_3.
11
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Superconducting Density of States in B-Doped Diamond

64%
Onufriienko O., Samuely T., Zhang G., Vanacken J., Xu Z., May P., Szabó P., Moshchalkov V., Samuely P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1033-1035
EN
In the presented work, we investigated the superconducting boron doped diamond polycrystalline film prepared by chemical vapor deposition by means of scanning tunneling microscopy/spectroscopy. Differential conductance spectra measured at various temperatures were used to obtain the values of superconducting critical temperature and energy gap. Comparing various theoretical models fitted to the differential conductance spectra measured at 0.5 K suggests weak pair breaking. However, this cannot account for the high 2Δ/(k_{B}T_{C}) ratio, which therefore indicates strong coupling.
12
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Point-Contact Spectroscopy of Superconducting MgCNi_3 Single Crystals

64%
Pribulová Z., Szabó P., Kačmarčík J., Samuely P., Jang D., Lee H., Lee H., Lee S.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
215-218
EN
The first point-contact spectroscopy measurements on MgCNi_3 single crystals of very good quality are presented. The measurements have been performed in the temperature range from 1.5 K up to 10 K and at magnetic fields up to 6 T. The superconducting energy gap Δ of the system is found to be scattered between 1 and 1.2 meV which gives the 2Δ/k T_c ratio between BCS weak-coupling value of ~3.5 and a strong coupling of about 4.2. The excess current evaluated in magnetic field indicates the presence of a single energy gap.
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