Preparation and characterization of thin films of the heavy fermion superconductor UPd2Al3

Huth, Michael; Kaldowski, A.; Hessert, J.; Steinborn, T.; Adrian, H.

doi:10.1016/0038-1098(93)90816-6

Cited by 42 publications

(24 citation statements)

References 11 publications

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“…Fitting the dc data of Fig. 2 yields a gap value E g = 1.9 meV, which corresponds to the one reported in [2,10,14]. From point contact measurements a larger gap up to 12.4 meV was suggested [15].…”

supporting

confidence: 77%

“…Based on this experimental evidence, UPd 2 Al 3 was described as a local-moment magnet and hence, the magnetic ordering should have only a minor influence on the electronic DOS. In this Letter we report on optical experiments at millimeter-submillimeter (mm-submm) wavelengths which clearly show the development of a pseudogap in the DOS in UPd 2 Al 3 below 25 K; our preliminary study on another film [9] showed the same features in the optical response; these findings cannot be easily explained by existing models.The highly c-axis oriented thin (150 nm) film of UPd 2 Al 3 was prepared on (111) oriented LaAlO 3 substrate (thickness 0.924 mm) by electron-beam coevaporation of the constituent elements in a molecularbeam epitaxy system [10]. The phase purity and structure of the film were investigated by X-ray and reflection high-energy electron diffraction.…”

mentioning

confidence: 99%

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Pseudogap in the optical spectra of UPd₂Al₃

Dressel¹,

Gorshunov²,

Kasper³

et al. 2000

J. Phys.: Condens. Matter

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The in-plane optical conductivity of UPd2Al3 was measured at temperatures 2 K < T < 300 K in the spectral range from 1 cm −1 to 40 cm −1 (0.14 meV to 5 meV). As the temperature decreases below 25 K a well pronounced pseudogap of 0.2 meV develops in the optical response. In addition we observe a narrow conductivity peak at zero frequency which at 2 K is less than 1 cm −1 wide but which contains only a fraction of the delocalized carriers. The gap in the electronic excitations might be an inherent feature of the heavy fermioin ground state.PACS numbers: 71.27.+a, 74.70.Tx, The heavy fermion (HF) compound UPd 2 Al 3 is one of the few materials which shows coexistence of superconductivity and magnetic ordering [1]. Susceptibility as well as resistivity data indicate the formation of a coherent state below a characteristic Kondo-lattice temperature T * ≈ 20 K; commensurate antiferromagnetic (AF) order develops below T N = 14 K, superconductivity sets in at T c = 2 K. For 2 K < T < 14 K the electronic specific heat shows a C el /T ∝ T 2 dependence; the effective mass of the charge carriers is estimated as m * /m 0 ≈ 50 [1,2] indicating strongly correlated electronic states in coexistence with the long-range AF order. It was suggested [3] that two different groups of uranium 5f states exist in UPd 2 Al 3 : one group is assumed to be rather localized and responsible for the magnetic properties whereas the states of another sort are less localized and responsible for the superconductivity of the compound.Optical experiments have proven to be sensitive to the formation of heavy quasiparticles [4]. In the HF compounds above T * the optical conductivity reveals a broad Drude behavior which characterizes normal metals. Below T * the increase in the density of states (DOS) at low energies is commonly described by the formation of a narrow Drude-like response with a renormalized scattering rate Γ * [5]. The signature of magnetic ordering in the optical response of heavy fermions was studied in Ref. [6]. In spin-density-wave (SDW) systems like URu 2 Si 2 , the opening of a single-particle gap in the electronic DOS at the Fermi surface is clearly seen in the optical properties [6,7]. No effect of the magnetic ordering was found in the infrared response of UPd 2 Al 3 so far. Neutron scattering results [8] reveal rather large ordered moments which reside predominantly at the uranium sites. Based on this experimental evidence, UPd 2 Al 3 was described as a local-moment magnet and hence, the magnetic ordering should have only a minor influence on the electronic DOS. In this Letter we report on optical experiments at millimeter-submillimeter (mm-submm) wavelengths which clearly show the development of a pseudogap in the DOS in UPd 2 Al 3 below 25 K; our preliminary study on another film [9] showed the same features in the optical response; these findings cannot be easily explained by existing models.The highly c-axis oriented thin (150 nm) film of UPd 2 Al 3 was prepared on (111) oriented LaAlO 3 substrate (thickness 0.924 mm) by ele...

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supporting

confidence: 77%

mentioning

confidence: 99%

Pseudogap in the optical spectra of UPd₂Al₃

Dressel¹,

Gorshunov²,

Kasper³

et al. 2000

J. Phys.: Condens. Matter

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“…[30] We have grown thin films of UPd 2 Al 3 using MBE techniques: evaporation of the three constituents U, Pd, Al and deposition onto LaAlO 3 (111) substrates. [4,5,26] The excellent quality of these thin films is evident from x-ray analysis of the lattice as well as from the temperature dependence of the dc resistivity, which reproduces the features known from bulk single crystals. we directly calculate the complex conductivity.…”

Section: Methodsmentioning

confidence: 61%

Microwave conductivity of heavy fermions in UPd2Al3

2010

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Abstract. Heavy-fermion compounds are characterized by electronic correlation effects at low energies which can directly be accessed with optical spectroscopy. Here we present detailed measurements of the frequency-and temperature-dependent conductivity of the heavy-fermion compound UPd2Al3 using broadband microwave spectroscopy in the frequency range 45 MHz to 40 GHz at temperatures down to 1.7 K.We observe the full Drude response with a relaxation time up to 50 ps, proving that the mass enhancement of the heavy charge carriers goes hand in hand with an enhancement of the relaxation time. We show that the relaxation rate as a function of temperature scales with the dc resistivity. We do not find any signs of a frequency-dependent relaxation rate within the addressed frequency range. PACS

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“…To avoid the extremely high reflectivity of bulk samples, we studied 150 nm thick epitaxial UPd 2 Al 3 -films deposited on LaAlO 3 substrates by molecular beam epitaxy [39]. The physical properties of these thin films have been characterized carefully and match those of bulk single crystals.…”

Section: Experimental Methods and Resultsmentioning

confidence: 99%

Verifying the Drude response

Dressel

Scheffler

2006

Ann. Phys.

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By now more than 100 years passed since Paul Drude suggested his highly acclaimed model of electronic transport. In the form advanced by A. Sommerfeld, the Drude model is still heavily utilized to describe, for instance, the optical properties of metals. Surprisingly, the key prediction of the Drude model, the frequency dependence of the complex conductivity with its pronounced roll-off was directly observed in an experiment only very recently. Here we present direct and independent measurements of both the real and imaginary parts of the metallic conductivity in a large range of frequency around the scattering rate.

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Preparation and characterization of thin films of the heavy fermion superconductor UPd2Al3

Cited by 42 publications

References 11 publications

Pseudogap in the optical spectra of UPd₂Al₃

Pseudogap in the optical spectra of UPd₂Al₃

Microwave conductivity of heavy fermions in UPd2Al3

Verifying the Drude response

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Preparation and characterization of thin films of the heavy fermion superconductor UPd2Al3

Cited by 42 publications

References 11 publications

Pseudogap in the optical spectra of UPd2Al3

Pseudogap in the optical spectra of UPd2Al3

Microwave conductivity of heavy fermions in UPd2Al3

Verifying the Drude response

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Product

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Pseudogap in the optical spectra of UPd₂Al₃

Pseudogap in the optical spectra of UPd₂Al₃