You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
thin superconducting films are characterized by reduced dimensionality and short coherence length , both of which contribute to the enhancement of fluctuations of the superconducting order parameter above the transition temperature .
these fluctuations are expected to affect both thermodynamic and transport measurements .
properties such as the specific heat , magnetization and electrical conductivity in the vicinity of the superconducting transition have been studied both experimentally  @xcite and theoretically .
@xcite in particular , fluctuation effects on the electrical conductivity were first discovered by glover,@xcite and the diagonal elements of the conductivity tensor ( or paraconductivity ) are now well understood following the original work of aslamazov and larkin @xcite , maki @xcite and thompson .@xcite owever , comparable experimental studies of the off diagonal ( all ) conductivity have been relatively limited in scope .    in this paper we investigate the longitudinal and all conductivities of ultrathin disordered tantalum nitride ( tan@xmath2 ) films as a function of perpendicular magnetic field close to and above the zero field critical temperature @xmath3 .
although both the longitudinal ( @xmath4 ) and all ( @xmath5 ) resistances vanish in the superconducting state , we find an enhanced all resistance above the superconducting transition temperature @xmath6 . such an enhanced resistance can be understood by considering dominant contributions of time - dependent fluctuation effects to the full conductivity tensor above @xmath0 .
the all effect at temperatures near @xmath0 has been studied in thin films of conventional superconductors such as mosi , moge , nbge , and amorphous ino ,  @xcite as well as in strongly anisotropic cuprate superconductors .
@xcite nevertheless , it is not well understood and continues to be a topic of active research .
@xcite for example , an unexpected sign reversal of the all voltage near @xmath0 has sparked considerable debate ( see e.g. refs .   and   and references therein ) .
owever , all of these studies have been complicated by vortex physics below @xmath0 or by contributions from the normal state all effect .
a number of microscopic and phenomenological studies have considered contributions due to vortices , pinning effects ,  @xcite and superconducting fluctuations .
@xcite efforts to reconcile these studies have been hampered by the difficulty of probing fluctuation effects in the all conductivity in conventional superconducting films .
challenges include the combination of high carrier concentration and large longitudinal resistance typical for such systems .
thus , no conclusive picture for the effect of fluctuations of the superconducting order parameter on the all conductivity in the normal phase has been reached . in this paper
we study field - dependent fluctuation effects in a regime where they may be unambiguously separated from vortex physics and from distinct normal state contributions .
thus , we provide a complete description of the all effect in a thin disordered film close to the phase transition into the superconducting state .
tantalum nitride films were prepared using sputter deposition onto a si substrate .
sample composition was analyzed using x - ray photoemission spectroscopy and determined to be @xmath7 at .
@xmath8 @xmath9 .
sample thicknesses were well controlled using the sputtering time and confirmed via x - ray reflectivity and tem measurements ; the sample thickness @xmath10 is 4.9 nm .
x - ray diffraction analysis showed no sign of crystalline order , and surface analyses showed no signs of granularity or inhomogeneity .
samples were patterned into all bar devices using standard optical photolithography techniques and ar - ion etching , and ti - au electrical contact pads were deposited using electron beam evaporation .
the active area of the devices is 400 @xmath11 m @xmath12 100 @xmath11 m .
linear longitudinal and all resistance were measured using standard four - point low frequency lock - in techniques in perpendicular magnetic fields ; care was taken to ensure that all measurements were linear in the excitation current . the all resistance was extracted from the component of the all voltage antisymmetric in the applied field , and was typically @xmath13  100 times smaller than the longitudinal contribution .
five devices fabricated from the same film were measured and all demonstrated qualitatively identical behavior ; the results presented in this paper are from two representative devices . throughout the paper
the longitudinal and all resistance and conductivity data and theoretical expressions are given in two dimensional ( sheet ) quantities .
2.75 k. the inset shows the measured fluctuation conductivity @xmath14 for this sample plotted versus @xmath15 computed using three values of @xmath16 ; the solid line depicts a slope of -1.33 which is expected for an al term that is percolation dominated . ]
to understand the hall effect , it is important to first understand the behavior of the longitudinal resistance . outside the superconducting phase and away from to the transition , the system is characterized by two types of low energy degrees of freedom : quasiparticles that are described using fermi liquid theory and superconducting fluctuations .
the normal state conductivity @xmath17 far from @xmath0 is attributed to the quasiparticles . in the vicinity of the transition ,
the fluctuations of the superconducting order parameter create a new channel for the electric current .
the main contribution of the superconducting fluctuations to the electrical transport can be formulated as the `` drude term '' for these degrees of freedom .
this contribution corresponds to the aslamazov - larkin ( al ) term .
@xcite to estimate the al term one has to find the lifetime of the superconducting fluctuations , @xmath18 , because the drude - like conductivity is proportional to it .
the finite lifetime of the superconducting fluctuations reflects the fact that outside of the superconducting phase the creation of a cooper pair costs energy . upon approaching the temperature - tuned superconducting transition
this energy becomes small , and @xmath18 grows as @xmath19 .
consequently , the al contribution to the longitudinal conductivity  @xcite is : @xmath20 in amorphous films with moderate disorder , the interaction between quasiparticles and superconducting fluctuations leads to an additional singular contribution to the conductivity .
similar to the al term , this contribution , known as the maki - thompson ( mt ) term ,  @xcite diverges as @xmath19 .
owever , the mt term depends also on the dephasing time @xmath21 : @xmath22 this contribution is expected to be less significant in inhomogeneous systems .
@xcite note that the two expressions given above correspond to films in which the superconducting fluctuations are essentially two - dimensional ( 2d ) , while the quasiparticles are three dimensional .     versus temperature
; here @xmath23@xmath24 was extracted at the point where the resistance approaches 50% of its normal - state value .
the slope @xmath25 1.7 t / k is extracted from a linear fit to the data , and the mean - field transition temperature @xmath26 2.8 k for this sample . ]    in fig .
[ fig : resistive ] we present the zero - field superconducting transition of sample 1 ; the normal state sheet resistance at 10 k is @xmath27 = 0.94 k@xmath28 . also shown in fig .
[ fig : resistive ] is the resistance measured in an applied field of 8 t , well above @xmath23@xmath29 5 t. the tan@xmath2 film studied in this work can be treated as two - dimensional with respect to superconducting fluctuations .
dense measurements of the resistive transition as a function of temperature and applied perpendicular magnetic field near @xmath0 on sample 2 , shown in fig .
[ fig : lowfield ] , were used to extract @xmath23@xmath30 1.7 t / k near @xmath0 .
the superconducting coherence length @xmath31 nm is larger than the film thickness , @xmath324.9 nm . all measurements indicate a carrier density of @xmath33 @xmath34 for both samples , from which we find that the bulk penetration depth is @xmath35 nm . in the presence of disorder
the penetration depth increases to @xmath36 nm , while for a 2d film the relevant magnetic screening length becomes @xmath37 nm .
the mean free path is estimated to be @xmath38 0.2 nm . measured and calculated
film parameters for both samples are summarized in table  [ tab : devparams ] .    [ cols="^,^,^,^,^,^,^,^,^,^,^ " , ]
in summary , we have performed careful studies of the longitudinal and all conductivities at temperatures near and above the zero - field superconducting transition in disordered films of tan@xmath2 .
studying fluctuation effects in the all conductivity is an experimental challenge in systems with high carrier concentration and large longitudinal resistance .
these measurements appear to be consistent with theoretical analysis over a wide range of temperatures and magnetic fields .
observation and verification of this effect may facilitate more careful studies of superconducting contributions to the all effect and provide a direct route to extract information about the particle - hole asymmetry of the superconducting fluctuations through the parameter * @xmath39*. finally , such an analysis provides a more precise technique for estimation of the temperature where the gap closes .
we would like to thank the staff of the stanford nanocharacterization laboratory .
this work was supported by national science foundation grants nsf - dmr-9508419 ( ak ) , nsf - dmr-1006752 ( amf ) and by a nsf graduate research fellowship ( npb ) , as well as department of energy grant de - ac02 - 76sf00515 .
amf and km were supported by the u.s .- israel bsf , and kst by nrap grant .
sample 1 . panel ( a ) shows the measured resistance in applied magnetic fields of 0 , 2 , 4 , and 8 t. panel ( b ) shows the calculated magnetoresistance @xmath40 as described in the text ; the continuous curves are guides to the eye , and the vertical bar indicates the approximate position of @xmath16 . ]    in many studies the normal state resistance is either weakly temperature dependent  @xcite or determined experimentally by applying a large magnetic field to suppress superconductivity and assuming a negligible normal - state magnetoresistance ( mr ) .
@xcite in our samples , a large nonclassical mr prohibits such an approach , and so we need a well defined procedure to account for it .
figure  [ fig : magres ] shows the resistance versus temperature of sample 1 up to 30 k for various values of applied magnetic field .
the lower panel of this figure shows the mr , defined as @xmath41 calcualted using these same data . according to kohler s rule@xcite , the classical normal state mr should be a universal function of @xmath42 , and in the low - field limit the mr @xmath43 , where @xmath44 is the cyclotron frequency of the electrons
, @xmath45 is their elastic scattering time , b = @xmath46 , and @xmath23 is the magnetic permeability . for our samples
@xmath47 , much smaller than the measured mr shown in fig .
[ fig : magres ] , and the low temperature mr does not scale as a universal function of @xmath42 .
while we expect superconductivity effects to give a large mr close to the superconducting transition , this behavior should decay to zero as the temperature or magnetic field are increased .
the measured mr at 30 k , well above @xmath48 2.8 k , is still three orders of magnitude larger than @xmath49 , and thus we must describe this large non - classical mr .
our first step in identifing the normal state resistance @xmath50 is to fit the data at 10 k @xmath51 t @xmath51 30 k and various magnetic fields with the following function : @xmath52.\ ] ] by interpolation we can find the phenomenological parameters a ( ) and t@xmath53 ( ) for arbitrary fields , and hence , obtain an expression for the normal state mr at all t and .
to now determine the normal state resistance at zero field , r@xmath54(t,=0 ) , we use the expression for the normal state mr given in eq .
( [ mr ] ) and the resistance measured at 8 t @xmath55 + 1}.\end{aligned}\ ] ] this approach necessarily recovers the measured zero - field resistance at high temperatures , assuming that deviations from the exponential temperature dependence of the mr at low temperature arise from superconducting fluctuations .
now we are fully equipped to estimate the normal - state resistance for any temperature and magnetic field @xmath56 both close and far away from the transition @xmath57 + 1}.\ ] ] recent studies  @xcite of fluctuation phenomenon in high-@xmath0 materials have used a similar approach to describe normal state behavior .
we have studied the hall effect in superconducting tantalum nitride films . 
 we find a large contribution to the hall conductivity near the superconducting transition , which we can track to temperatures well above @xmath0 and magnetic fields well above the upper critical field , @xmath1 . 
 this contribution arises from aslamazov - larkin superconducting fluctuations , and we find quantitative agreement between our data and recent theoretical analysis based on time dependent ginzburg - landau theory .