Papers by Erwin Schuberth
Journal of Low Temperature Physics
International Journal of Modern Physics B, Feb 15, 1996
The emphasis of this article lies on the properties of heavy fermion systems at the lowest temper... more The emphasis of this article lies on the properties of heavy fermion systems at the lowest temperatures obtained so far. Methods for measuring specific heat capacity and magnetic susceptibility in the milliKelvin regime are described for both low magnetic fields (<20 mT ) and high fields (<8 T ). Experimental results on UPt 3, UBe 13, and CeCu 6, are presented, and remaining problems are discussed. UPt 3 is widely regarded as the heavy Fermion system which exhibits unconventional superconductivity as demonstrated by the existence of multiple superconducting phases. Whether power laws for instance for the specific heat capacity in the superconducting state extend to T ≈ 0 instead of an exponential behavior as for BCS superconductors is a long-standing question. We have measured the specific heat capacity of several single crystals of UPt 3 in magnetic fields varying from 0 up to 7 T down to a final temperature of 10 mK . Instead of an extended power law a maximum of c(T) occurs around 20 mK, and this maximum persists in magnetic fields above B c2. It is obviously due to a new phase transition which is present both in the normal and in the superconducting state of UPt 3, slightly modified in the latter. Entropy balance above T c is fulfilled if the low-temperature peaks are included. DC-magnetization measurements on two single crystals of UPt 3 in a SQUID system yield a temperature dependence of the penetration depth ~T2 between 150 and 20 mK, considerably extending the temperature range of earlier experiments. Measurements of the anisotropic part of the magnetic susceptibility in a torque-meter indicate an additional phase line from a temperature-dependent anisotropic susceptibility to a T-independent state which is closely connected to the Bc2-line over a wide field range. No indication for a re-entrance of superconductivity is found down to 20 mK. For UBe 13 (in the superconducting state) no specific heat anomaly above 24 mK is found but a deviation from the T2.7 power law valid at higher temperatures. On a single crystal of CeCu 6 dc-magnetization measurements in various magnetic fields in a SQUID system show a plateau of the magnetic susceptibility between 400 and 50 mK, followed by an increase towards lower temperatures. An attempt to fit the low-temperature magnetization curves in several fields between 0.01 mT and 1.6 mT (minus the background from the plateau) with a Brillouin function revealed significant deviations. In 2.7 mT, the highest field applied in this experiment, however, the magnetization can be perfectly fitted assuming a tiny concentration of Gd impurities (1.5 ppm). After subtraction of the contribution due to the Gd 3+ ions from the magnetization curves in each of the lower fields a drop is revealed below 3–5 mK which gets successively quenched by the magnetic field and which has disappeared in 2.7 mT. The specific heat capacity of the same single crystal of CeCu 6 in zero magnetic field shows an increase of c/T from 1.55 J/moleK 2 at higher temperatures up to 2.8 J/moleK 2 at 11 mK. We interpret both results as due to an antiferromagnetic phase transition at 3–5 mK with the peak just not reached in the specific heat experiments.
Eur Phys J B, 2005
Solid 3 He, in the bcc lattice between 34 and 100 bar, exhibits two nuclear magnetic ordered phas... more Solid 3 He, in the bcc lattice between 34 and 100 bar, exhibits two nuclear magnetic ordered phases in the sub-mK temperature range, the so called U2D2 low (magnetic) field phase and the "high field phase" above 0.4 T. To determine the exact spin structure of these phases we started a project of neutron scattering from the ordered solid in collaboration with the Hahn-Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 µK (or even twenty times lower in the case of the hcp lattice which is formed above 100 bar) and to keep it there long enough to measure a magnetic neutron reflection. We studied the growth of crystals in Ag sinters of different pore size and with different growth speeds to find an optimal way to obtain single crystalline samples. As a first diagnostic step we performed pulsed NMR measurements in the ordered phases of solid 3 He in a sinter of 2700Å particle size down to temperatures of 450 µK at various molar volumes. We could keep the samples in the ordered state for as long as 140 h. The second method we used was SQUID magnetometry. For the low field phase TN was indicated by a drop of the intensity, both in the NMR signal and in the dc magnetization, whereas in the high field phase an increase of about 30% was observed below the ordering temperature. For the fabrication of the sinters a packing fraction of 50% and subsequent annealing proved to be very favorable to obtain cold ordered solid. Furthermore, we find that a paramagnetic surface contribution from a few monolayers of 3 He exists down to 500 µK in addition to the bulk magnetization.
Japanese Journal of Applied Physics Supplement, Aug 19, 1987
AIP Conference Proceedings, 2006
ABSTRACT To determine the exact spin structure of the nuclear magnetic ordered phases of solid 3H... more ABSTRACT To determine the exact spin structure of the nuclear magnetic ordered phases of solid 3He, the U2D2 low field and the high field phases above 0.4 T, a European Research and Training Network for neutron scattering from the ordered solid was established which consisted of a collaboration with the Hahn Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 muK and to keep it cold long enough to measure a magnetic neutron diffraction. The sinter is also necessary to absorb the major part (> 90%) of the heat generated by the neutron capture and decay reaction of the 3He nucleus. In this work we studied the growth of crystals in Ag sinters of different pore sizes and with different growth speeds to find an optimal way to obtain single crystalline samples, or at least samples with only a few grains. We used SQUID magnetometry and NMR to measure the magnetization in the ordered phases. They were indicated by the known drop of the intensity, both in the NMR signal and in the dc magnetization, for the U2D2 phase, and by an increase of about 30% for the high field phase. The best results for cooling were obtained with sinters made from 700 Å ``Japanese powder'' with a packing fraction of 50% which were annealed at 130 °C after sintering and then had a calculated particle size of about 4200 Å. In the dc magnetization we found a paramagnetic surface contribution from a few monolayers of 3He down to 500 muK in addition to the bulk magnetization.
Science (New York, N.Y.), Jan 29, 2016
The smooth disappearance of antiferromagnetic order in strongly correlated metals commonly furnis... more The smooth disappearance of antiferromagnetic order in strongly correlated metals commonly furnishes the development of unconventional superconductivity. The canonical heavy-electron compound YbRh2Si2 seems to represent an apparent exception from this quantum critical paradigm in that it is not a superconductor at temperature T ≥ 10 millikelvin (mK). Here we report magnetic and calorimetric measurements on YbRh2Si2, down to temperatures as low as T ≈ 1 mK. The data reveal the development of nuclear antiferromagnetic order slightly above 2 mK and of heavy-electron superconductivity almost concomitantly with this order. Our results demonstrate that superconductivity in the vicinity of quantum criticality is a general phenomenon.
Aps March Meeting Abstracts, Mar 1, 1996
Physica B Condensed Matter, May 1, 2003
To obtain the exact spin structure of the nuclear magnetically ordered phases of solid 3 He; in t... more To obtain the exact spin structure of the nuclear magnetically ordered phases of solid 3 He; in the BCC lattice called U2D2 and high field phase, both occurring below about 1 mK; we started a project of neutron scattering from the solid at the Hahn-Meitner Institut, Berlin. This experiment faces three main difficulties: to cool the solid to temperatures below 1 mK (or even much lower in the case of the HCP lattice), to keep it there under neutron flux, and to grow a single crystal within the sintered material needed for this purpose. As a first step we have performed pulsed NMR measurements in the ordered phases of solid 3 He in a silver sinter of 700 (A particle size down to temperatures of 600 mK at various molar volumes. The samples remained in the ordered state for as long as 110 h:
International Journal of Modern Physics B, 1996
The emphasis of this article lies on the properties of heavy fermion systems at the lowest temper... more The emphasis of this article lies on the properties of heavy fermion systems at the lowest temperatures obtained so far. Methods for measuring specific heat capacity and magnetic susceptibility in the milliKelvin regime are described for both low magnetic fields (<20 mT ) and high fields (<8 T ). Experimental results on UPt 3, UBe 13, and CeCu 6, are presented, and remaining problems are discussed. UPt 3 is widely regarded as the heavy Fermion system which exhibits unconventional superconductivity as demonstrated by the existence of multiple superconducting phases. Whether power laws for instance for the specific heat capacity in the superconducting state extend to T ≈ 0 instead of an exponential behavior as for BCS superconductors is a long-standing question. We have measured the specific heat capacity of several single crystals of UPt 3 in magnetic fields varying from 0 up to 7 T down to a final temperature of 10 mK . Instead of an extended power law a maximum of c(T) occurs...
To determine the spin structure of the nuclear magnetic ordered phases of solid ^3He, neutron sca... more To determine the spin structure of the nuclear magnetic ordered phases of solid ^3He, neutron scattering would be the method of choice. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 0.5 mK and to aborb the major part (> 90 %) of the heat generated by the neutron capture. In this respect we studied the growth of crystals in Ag sinters of different pore sizes to find an optimal way to obtain preferably single crystalline samples. The ordered phases were indicated by a drop of the NMR intensity for the U2D2 phase and by an increase (30 %) for the high field phase. Just below TNeel (0.9 mK) we found a line splitting as expected for the U2D2 phase a) of about 20 kHz to the high frequency side of the Larmor line at 1980 kHz and b) 4 kHz on its low frequency side at 240 kHz. For unknown reasons the Larmor line itself was absent in the U2D2 phase. In the paramagnetic phase T2 turned out to be abou...
Physical Phenomena At High Magnetic Fields IV, 2002
Simultaneous measurements of magnetic susceptibility from 0.5 to 10 mK and pressure from 2.88 to ... more Simultaneous measurements of magnetic susceptibility from 0.5 to 10 mK and pressure from 2.88 to 3.54 MPa have been made in 3He nanoclusters embedded in a 4He matrix, following phase separation. The susceptibility of the 3.54 MPa, all –solid sample behaves similarly to that of bulk 3He for v = 21.3 cm3/mole, with a Weiss constant θ = -250μK. For the 2.88 MPa, liquid-droplet sample, θ = 140μK, indicating a ferromagnetic tendency, similar to 2-D films at some coverages. At intermediate pressures, χ has a peak near 1.05 mK, but without a discontinuity. For all samples, χ had a solid-like contribution to the lowest temperatures. Magnetic ordering in nano-clusters appears to be different than the U2D2 phase of bulk 3He.
Physical review letters, Jan 6, 1992
ABSTRACT We have observed large specific-heat anomalies around 18 mK in two single-crystal sample... more ABSTRACT We have observed large specific-heat anomalies around 18 mK in two single-crystal samples of UPt3 of different origin. These indicate additional forms of order which still take place in the electronic system of the heavy-fermion compound at these low temperatures. Since magnetic-susceptibility measurements showed that the samples remain superconducting, the new ordering coexists with superconductivity.
Physical review. B, Condensed matter, 1995
ABSTRACT dc-magnetization measurements in various magnetic fields on two samples from the same si... more ABSTRACT dc-magnetization measurements in various magnetic fields on two samples from the same single crystal of CeCu6 in a superconducting quantum interference device system show a plateau of the magnetic susceptibility between 400 and 50 mK, followed by a Curie-like increase towards lower temperatures. At very low temperatures the magnetization starts deviating from a 1/T behavior, saturating around 900 μK in 2.7 mT, the highest B/T ratio obtained in this experiment. We show that this Brillouin behavior must be due to a tiny amount of the magnetic ion Gd3+, present in a concentration of 1.5(3) ppm. After subtracting this contribution from the magnetization curves in various lower fields, a field-dependent structure with a drop of the magnetic susceptibility around 3 mK is left. This decrease is reduced with increasing field and has vanished in 2.7 mT. In the lowest fields the structure is very similar to one observed in ac-susceptibility measurements. The fact that this drop of χ occurs in different samples and that it can be quenched by the magnetic field points to an intrinsic antiferromagnetic ordering in CeCu6 around 3 mK. We cooled one sample to a lowest temperature of 450-10+40 μK in a field of 0.3 mT. The susceptibility further decreases with decreasing temperature and shows a small shoulder at 650 μK. In addition, we measured the specific-heat capacity of the same single crystal of CeCu6 in zero magnetic field down to a temperature of 11 mK. Between 40 and 11 mK c/T increases from 1.55 to 2.8 J/mole K2, most likely an indication of the high-temperature end of the magnetic transition.
Physical review. B, Condensed matter, 1988
... D. Meschede, F. Steglich, W. Felsch, H. Maletta and W. Zinn, Phys. Rev. Lett. 44, 102 (1980) ... more ... D. Meschede, F. Steglich, W. Felsch, H. Maletta and W. Zinn, Phys. Rev. Lett. 44, 102 (1980) [SPIN];[INSPEC];[CAS]. KA Mirza and JW Loram, J. Phys. F 15, 439 (1985) [CrossRef]. T. Fujita, K. Satoh, Y. Onuki and T. Komatsubara, J. Magn. Magn. Mater. 47&quot; &amp; bold &quot;48, 66 (1985). ...
Physica B, 2000
We have investigated the feasibility of neutron di!raction from solid He. The experiment will be ... more We have investigated the feasibility of neutron di!raction from solid He. The experiment will be performed at the HMI, "rst aiming for the properties of the antiferromagnetic ordering in the BCC phase and the ferromagnetic order in the HCP phase. Signal and beam heating considerations are essential to account for the enormous neutron absorption cross section of He. The study shows that neutron di!raction and transmission experiments are possible, relying on the experience gained from the neutron di!raction experiments on Cu and Ag at nanokelvin temperatures. A pressure cell has been developed which complies with the con#icting demands arising from the neutron and ultralow temperature aspects of the experiment. This work is a "rst step in an extensive e!ort to characterize He by neutron di!raction.
Physics Letters A, 1986
ABSTRACT The nuclear spin-lattice relaxation time in thallium metal has been measured from 0.4 to... more ABSTRACT The nuclear spin-lattice relaxation time in thallium metal has been measured from 0.4 to 75 mK in magnetic fields from 18 to 1000 mT. The value of the Korringa constant k = T1T is 4.37(8) ms K. It is independent of field and temperature over the ranges investigated and differs significantly the previously measured value. On leave from Physics Department, University of British Columbia, Vancouver, B.C., Canada V6T 2A6.
Solid State Communications, 1983
... 3. Using the equation states can create a soft gap in the density of states near axx = (a Ta)... more ... 3. Using the equation states can create a soft gap in the density of states near axx = (a Ta) exp (To T)7 (3) EF, which also leads to a temperature dependence of the form ax., exp (To T)1 2. Unfortunately no infor with the free parameters 3 and y we ... 9. AL Efros BI Shklovskii,J. Phys ...
Review of Scientific Instruments, 1984
ABSTRACT Superconducting heat switches consisting of tin and indium wires pressed between machine... more ABSTRACT Superconducting heat switches consisting of tin and indium wires pressed between machined silver rods and oriented parallel to the operating magnetic field are described. Their advantages are simplicity of design and physical smallness. Thermal conductivities of such switches in the normal and in the superconducting state are reported.
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Papers by Erwin Schuberth